How do you become a professional actor in Hollywood without knowing any people in the entertainment industry?

Truth is, you don't.  But the answer is in how you define connections.  (and certainly also how your define "big", but I won't go into that). If you mean, your-uncle-is-Spielberg type connections well, then, yeah, that's a hella bonus, but really this is a business based on relationships - all of them. Movie crews are upwards of 40 people at any time on set, not including above-the-line crew members (producers, directors, actors, writers, executives, casting directors), so part of the art of being an actor is being a team player. I'm not going to discuss talent and training - because you didn't ask that question - so I'll just assume an "actor", as defined, has plenty of both and move past it. The best thing to do when you come to Hollywood is to jump into a class that will surround you with fellow team-members (I say team - not just actors - because it is really valuable to know directors, writers, editors).  Also, to get involved in activities which will bring you close to more of these people - if you play softball, get into a league, go to industry meetups, conventions, panels, etc.  Get a "B" job that gets you next to more people creating in the industry.  It's really easy to do that in Hollywood.  Your neighbor, the guy at the corner cafe, almost everyone is part of this industry - it's a unique city that way.  These are your connections.  Just get out of the house.  Put your work out there.  Over and over again.  Let people know that you're serious about this.  Get a group of fellow actors together and make a short film, post it.  Then make another.  Put up a play.  Plenty of people have made it "big" without already having connections prior to landing in Hollywood -- however, almost no one has made it big without ever having built any at all.  "Connections" is just another word for friends.

good question . and you already have good answers from previous people. I do recall that Bruce Willis was simply noticed by a director in the bar where he worked as a bartender in NYC . that director was looking for a specific look and he loved what he saw in Willis . Charlize Theron had similar story when she simply came to auditon ... those are rear , you would have it if by Chance someone is looking for your exact look.  otherwise , connections will help , just notice why Cameron and Nolan work with same actors ?

Yes. Take the best classes so you are prepared to stand out when you audition. My students work all the time because they are talented and probably more important, they have excellent technique. Then get into every theater and film production you can to make contacts, get credits and get footage for your reel. When all this is done then send your resume to dozens of agents and (unfortunately and to me immorally on the part of casting directors), go to casting sessions you have to pay for. But only when you are ready. Read my book called How to Make Your Audience Fall in Love With You. Learn how to present yourself at auditions. Don't prepare in front of them with a sigh or taking a moment. Start! Make your first line strong and not just a lead up to the scene. Know what you are fighting for and how you want your partner to change. Make risky choices. In my book I talk about the part of a bank robber. One threatens people and runs to his car with the money. The other winks at a scared kid, flirts with the women, opens his eyes wide with glee when he sees the money. They have the same lines but which would you rather hire? Always use some kind of humor. Don't act weary or nasty even if you think the script is calling for that. It isn't. We want to fall in love with actors. Put a button on the scene by sending your partner a final message and then turn to the auditors. Get coached for big auditions. Turn up on time and answer your phone within an hour of a call. http://DerynWarren.com. I love actors. You are a brave lot. I wish you all the best.