A novel resonator structure for solid state laser is proposed. A lens with short focal length is introduced in the resonator, and the laser crystal (thermal lens) is put at its focusing point, so a special lens set is composed . By using the transform circle approach it is found that the lens set functions as an optical ‘ballast’. With adjusting one end mirror along optical axis adaptively such a resonator may guarantee TEM00 mode dynamic stable operation of high-power solid state laser while thermal focal length varies within a wide range. While the beam spots of TEM00 mode at the laser crystal and end mirrors keep unchangeable.