Passive coaxial spherical cavity is introduced by using a general matrix.In view of the thermallens effect in the cavity of solidstate laserthe closure conditions of thermal lens optical cavity was obtained by using symbolic operation of Matlab.The automatic closed thermal stable cavity model was establishedcombining the closure condition with the thermal lens effect model of optical cavity.The mirror curvature radius was changed adaptively by controlling the deformable mirror with the increase of pumping powerthus could make the output of resonant cavity of solidstate laser stable.