General speaking, brake fluid should be changed every 30-40 kmi

Re: 刹车油应该多少迈换呀？有什么办法检查该不该换呢？

General speaking, brake fluid should be changed every 30-40kmi. If you don't do it, you won't see much problem, however, something you should know:

1) Brake fluid has the charactor of absorbing moisture from air. Overtime, your brake fluid will contain certain percentage of water; consequently, the braking efficiencty will be lower - when you run on the road/applying braking, the brakes are very hot and water becomes evaporized, you are having air in the system.  You'll feel the brake pedal being softer, requiring brake pedal travelling longer distance for you to stop; some times this could lead to a safety issue.

2) Because of water, when the brake pistons are supposed to be fully back to base but they won't, continuing to apply pressure to rotors, that is "dragging", you'll lose gas mileage at the least.

Chaning brake fluid involves "bleeding". If you know how to do it, it's fairly simple, but need two persons to do it; or you can go parts stores to buy a vacuum bleader, so one person can do it.

I always do it myself so I don't know how much shops charge (per car brand, model and conditions).