Optical cavity is the very important component of frequency stabilizin g laser.The laser with narrow line-width is suitable for efficient cooling atoms,high-precision spectroscop y and accurately measurement.In the paper,a three-mirror ring optical resonator is proposed,in order to optimize the performance of our diode laser.On the basis of optimized mode matching between the incident laser and the cavity, a frequency reference for locking the laser is researched.Firstly,the laser waist spot size of 100μm is obtaine d by the propagation law of the fundamental mode Gaussian beam in space.Based on the optical matrix transformat ion law,the optical waist size of the ring cavity is 247.6μm,and it lies between two planar mirrors.Secondl y,according to the waist transformation rule of Gaussian beam passing through lens,a matching lens is pr oposed.Its focal length is 186mm and its waist position of 382mm away from the optical waist of the cavity.T hen this lens is applied to realize the optimal match between laser beam and the ring cavity.The experimental resul t shows that the line-width of transmission signal is 0.7MHz.Compared with the 200mm length short cavity with linewidth 1.5MHz,the result above is better and illustrates the superior performance of the ring cavity.The research on the optimal matching between laser and ring optical resonator is beneficial to the further optimizati on of laser linewidth.