The invention relates to a brake, in particular to a wet brake for a tractor. The brake comprises a shell body, pistons, friction piece components, friction limit mechanisms and piston return mechanisms, wherein each friction limit mechanism comprises a friction positioning rod, a friction resistance ring and a first clamping spring; each friction positioning rod is provided with a first positioning shaft shoulder and a second positioning shaft shoulder from left to right; each friction positioning rod is connected with the corresponding friction resistance ring through a friction pair; each piston return mechanism comprises a pull rod and a disk spring; each pull rod is connected with the shell body in a sliding way; the right end of each pull rod is in threaded connection with the corresponding piston; the sum of the static friction between each fiction positioning rod and the corresponding friction resistance ring is greater than the sum of the maximum force of all disk springs. By the wet brake for the tractor, the dragging caused by a return gap can be overcome effectively, the service life is prolonged by over 20 percent, the automatic compensating function for the abrasion of a friction piece is provided, the return gap of each piston is kept at the range of 0.4-0.6 mm all the time, and the problems that the brake response time is long and the liquid amount required for braking is deficient caused by an over-large brake gap are avoided.