In order to investigate the practical braking ability of united brake system with permanent magnet type eddy current retarder and exhaust brake in vehicle, the advantages and disadvantages of permanent magnet type eddy current retarder and exhaust brake were analyzed, respectively. The experiments and theoretical analysis on the braking ability of united brake with permanent magnet type eddy current retarder and exhaust brake for vehicle were carried out under the conditions of level roads and hillside paths. The results show that the united brake can make the braking distance shortened, the deceleration increased, the braking ability of the vehicle improved on the level road, and the united brake system can meet the demands for vehicle to travel on steeper slope at steady and economic speed. All of above that can provide reference for application of the permanent magnet type eddy current retarder and exhaust brake in vehicle.