This is difficult to answer directly, so here's some information that may help.

It's a yes and no situation which will partly be affected by your landlord. If you have a 1 year lease and you stay for less than 6 months, as far as I know the landlord can decide to keep your deposit as compensation for you leaving the contract early and legally I don't think there is much you can do about it unless you made an "out clause" in the contract before hand.

After 6 months of staying, if you give your landlord notice (I think it's at least 1 month) that you will need to leave, you can negotiate the contract again and it's easier to get your deposit back, especially if the landlord hasn't lived up to the agreement (ie, I ask him to fix this, he didn't even though it says in the contract...) and then legally there is grounds to get your deposit back.

Overall though, it basically comes down to your landlord. If you have a really good reason (I must go back to my home country) or offer to find someone to take over the lease, they might be more willing to return the deposit. It depends on the situation though. I believe legally after 6 months of stay, assuming you have paid on time and didn't destroy the apartment, and you have a legitimate reason for breaking the agreement early, there is some legal backing you can use to get the deposit back.

Please note however that the rules and laws are different every 5 meters here in China, so it will depend on where you live.

Rent your place to others

I had my deposit back. But I (still) have very good, friendly relations with the landlady, had been living there for a long time, taking good care of her apartment, and I was paying the rent until she found another person for my place (which was fast). And I had a really good reason to move out.I would not expect to much cooperation from the landlord side otherwise, because for him/her it's a trouble. I guess the contract should specify this and all the rest is a matter of good will of the landlord.