Compared with widely-used liquid crystal spatial light modulators, digital micromirror devices (DMDs) have advantages in fast switching speed, high precision display, polarization-independent, high diffraction efficiency, and broadband capability. Therefore, we attempt to apply DMDs as wavelength selectors to tunable fiber lasers and analyze the dependence of diffraction properties of the two-dimension DMD grating on the incident angle, pixel spacing, etc. The diffraction orders and intensity distribution of DMDs in 0.7″ and 0.55″ sizes with different pixel spacings are discussed in detail. The theoretical results show that under the experimental constraint condition, a 0.7″ DMD allows four orders interference irradiance maxima. However, the light intensity is relatively weak due to the condition of far away from “blazed” grating. For a 0.55″ DMD, most of the diffracted radiation is concentrated in one order due to the approximate “blazed” condition. So, a 0.55″ DMD grating as a wavelength tuner is a better choice for the stability of laser systems.