Abstract: In order to improve the thermal stability of V-type resonant cavity, based on graphic analysis, a simple V-type folded cavity was transformed into a coaxial spherical cavity with a thin lens. At the same time, considering the thermal effect of lens and combining with equivalent cavity analysis method of multi element optical resonator, the V-type folded cavity with lens group was transformed into a coaxial spherical cavity with no lens in the cavity. And the thermal stability of coaxial spherical cavity with no lens was calculated and analyzed. The results show that, the cavity has the widest range of thermal stability when the total cavity is 75mm and the fold angle is 0.15π. When the interval between the gain medium and folding mirror is 28mm, the focal length of the minimum thermal lens being suitable for the cavity can reach 12mm. The study shows that the key parameters of the cavity are important to thermal stability, and it has guiding significance for the optimization design of laser cavity stability.