The cause, criterion and research method of small-scale self-focusing on high-power laser systems are reviewed. Small-scale self-focusing of lasers in Ndglass and frequency-conversion crystal are analyzed and discussed. Moreover, measurement of small-scale modulation growth is introduced. Then methods to suppress small-scale self-focusing are also presented, and damage of high-power lasers to optical components is reduced by controlling small-scale modulation growth. Finally, the future research in nonlinear effects of fused high-power laser technology is proposed.