The invention provides a tri-spindle synchronizer, which is characterized in that sliding bearings are respectively arranged on positions corresponding to a front end cover and a rear end cover; two ends of a drive shaft and a driven shaft which are arranged in parallel are arranged in the holes of the sliding bearing; three oil cavities and two clapboards are fixedly arranged between the front end cover and the rear end cover, and the clapboard is arranged between the oil cavities; an oil inlet is arranged in the middle oil cavity, and an oil outlet is respectively arranged on the other end of each of the oil cavity; an oil cavity passes through all the oil cavities and the clapboards and is communicated with the oil inlet; three drive wheels are arranged on the drive shaft, three drivenwheels which are engaged with the drive wheels correspondingly are arranged on the driven shaft, and one pair of engaged gears are arranged in one oil cavity; and each oil cavity is provided with a high-pressure cavity and a low-pressure cavity.