The motor speed reducer is a widespread used motor dynamic system product. Its energy specification, system design match, application operation and maintenance and so on, serious influence energy efficiency. The low efficiency type increases consumes the electrical power. But the user does not understand clearly. Therefore the energy efficiency test of the motor reducer is an urgent topic. In order to promote the motor speed reducer energy efficiency, two type helical gear speed reducers are tested. The motor power are 0.5hp, 1hp, 2hp and 3hp respectively and reducer ratio are 10, 20 and 30, they are arranged in pairs. A brake method is established to measure the energy efficiency of motor speed reducer. Two different brands speed reducers are measured for 24 samples. The test results showed that A brand helical gear speed reducer at 100% load condition the most high energy efficiency are 85.24% for 2 Hp and 1:10 ratio, and 93.45% for 3 Hp and 1:20 ratio, 92.55% for 3Hp and 1:30. ° For B brand helical gear speed reducer at 100% load condition the most high energy efficiency are 87.35% for 3 Hp and 1:10 ratio, and 88.4% for 3 Hp and 1:20 ratio, 91.48% for 3Hp and 1:30.