The influence of thermal lens on the width of dynamic stabilization, angle of divergence and output mode of solid-state laser with asymmetry flat-flat cavity was analyzed by using transition circles theory. Compared with the ABCD matrix method which need a large number of computations, this method was relatively simple and the result was easily understood. Moreover a simple method to measure the length of thermal focus is given developed from this theory. By properly designing the parameters of resonant cavity, steady 10 W quasi-TM 00 mode CW output was achieved when the pumped power was 21 W. The mode and length of thermal focus of laser were measured. The experimental result was in accordance with theory.