Under the study on rod Nd-glasses heat-capacity laser thermal lensing,the general expressions of the thermal focus length are derived. The self-adjusting compensation is presented in theory. Using the characteristic of Nd-glasses, self-adjusting compensation system for thermal lens focus is designed to weaken the effect of the thermal lens on light pumping glasses heat-capacity lasers. Thus, a stable output spot radius can be achieved while the thermal lens focus varies in a broad range. In order to study the effect of heat-capacity laser thermal lensing, a wavefront curvature sensor comprising a phase defocus grating is used to measure the focus length. The result indicates that the heat exchange sets up a heat balance in about 20 s after pumping. With the increases of the numbers of pumping pulses, the thermal focus length deceases.