Abstract: In conventional mode selection method, the mirrors often used in laser cavity. In this paper, a new method that the diffractive optical elements, such as the diffractive mirrors, are used to substitute the traditional spherical mirrors is introduced. According to spectrum theory, the function of mode selection of diffractive mirrors is analyzes. Experimental results show that the properly selecting the cavity length and the aperture of the diffractive mirrors can obtain the higher diffractive loss ratio of 1:430 between the fundamental mode and TEM01 mode.