I eventually got a few offers from prop desks of large banks. But their bases are all pretty low. For example, one guy only agrees to pay 100K base + 60K guranteed bonus for this year. They told me that I might receive a bonus around two times or three times of my base if the group is doing well in the future. Is it true that prop desk tends to pay lower base as this? Thanks.

Which currency and which level of experience?

Can happen. Some places have a policy of relatively low fixed for pretty much everyone.But a more precise answer as Z says, requires more data.

US dollars. The job is in NYC. The offer is from one of the top Investment banks in US. Another offer is 120K base from another top bank. But the second one is not from prop desk. Does it make sense to take a 20% cut to join a prop desk?

Well, again your details are too brief to comment. However prop quant jobs are fairly risky - more of high return , high risk kinds as compared to regular desk quants or research quants ( sort of middle office). A job in my opinion is like investment , it is an investment of time, talent and the money (that you would make or forego - sort of opportunity cost). You have to keep in mind the market conditions, when you get in and what you want to do in the long term. With no experience in quant finance, if you end up loosing your job in the prop trading desk world by the end of the year, then it is not going to do help much. This is possible if your group does not make money in this volatilie market. On the contrary if you feel you have confidence in the prop trading desk,and that is what you want to do, then it is worth taking that risk. 20k is not much especially after taxes. Besides, you don't mention as to how much bonus you shall be making in the second job. A 60k bonus at the prop desk is not bad for first year with no experience. Definetly a bit low but not bad at all....

It seems strange to me that there is any job where you can know at the beginning of the year how much you will have made at the end of the year. It can only be produced artificially, by paying someone else to absorb your risk. Where a young person finds the money to hire an old person to absorb his risk, I don't know. I guess it is some kind of diversification pool.I guess it really would suck, though, if you couldn't afford to show up at the Black-and-White Ball in a Lamborghini. So sometimes it is best to know exactly how many beats you will miss in advance, so as to limit it to an acceptable level.