The kinetics mechanisms of additive hyrdogen in CuBr lasers are investigatedsystematically.There are two important mechanisms for increasing laser power afteradding hydrogen:(1)The gas temperature and CuBr vapor density at the center of lasertube are reduced, it decreases collision energy depletion of electron and leads to increaseelectron temprature;(2)Electron density increases during the pulse, the skin effect andthe" black center" of laser are improved. There is an optimum range of additivehydrogen, which is observed in the experiment. The mechanism is that with the gas temperature further decreased, the copper density and electron temperature are also decreased, it will restrain the population of the laser levels.