We studied on reducing backrush in no-loading and investigated on the factors affecting the in loading for 3K-type Paradox gear reducer. The gear reducer is composed plastic micro gears. In no loading, backrush is reduced by changing in the transportation coefficient for planet gears. In loading, backrush of this reducer grows lager with loading value, and backrush in no-loading is much smaller than that of in loading. The principal factors of backrush in loading are clearance between carrier and two internal gears, and transformation of rotary internal gear.
