A graphic analysis method is used to analyze the working characteristic under the effect of thermal lens of laser medium of a Z type folded laser resonator. The relationship of laser mode parameters bt、b2、b3 and beam waists wt、w2、w3 varied with focal length of thermal lens are obtained. The results shown that this type of resonator has a wider thermal stable range compared with other similar resonator, the stable range and beam waists can be changed by adjusting the parameter of resonator, in which the key parameter is the length l0+f1 of first arm. For the given resonator mirrors, the shorter l0+f1, the wider thermal stable range, and the smaller wt is. The length of second arm has a similar effects on stable range and beam radius.

solid state laser; Z type folded optical resonator; beam waist; graphic analysis