Based on the principle of passive mode-locked laser, combining the physical characteristics of the equivalent fast saturable absorber in self-mode-locked solid-state laser, the self-mode-locked dynamic equation and rate equations for controlling the running states are presented. With making the rate equations linearized, starting condition of self-mode-locked laser is derived. The direct relation between self-mode-locked starting condition of Kerr-lens mode-locked solid-state laser and self-mode-locked starting factor is firstly presented. Theory is good in agreement with the experimental results.