There are many kinds of nonlinear effects in the interaction between high power laser and matter. The beam of laser fusion driver is highly coherent, which greatly enhances the nonlinear effects, and inevitably limits the laser power and efficient utilization. Looking back on the development history of laser fusion driver, there is a dark line runing through the main line of improving laser output capability, which is struggling with beam coherence. The control status of beam coherence in laser fusion driver is reviewed from two aspects: restraining the nonlinear transmission effect of high power laser and suppressing the interaction between laser and plasma. In view of the potential demand, innovative technologies for the future development of high power lasers are proposed.