According to the rigorous coupled-wave theory(RCWA) and dielectric slab waveguide theory,the grating microstructure of a single crystal ZnO-based DFB laser diode in the 1550nm wavelength communication band was proposed.A two-dimensional electric field mode and wavelength linewidth were analyzed.The influence of the grating structure variation on the property of the single longitudinal mode transmission was obtained.Numerical simulation shows that the whole electric field energy reaches about 8.3×107 J when the spectral linewidth is smaller than 0.1 astron,the grating period is 489 nm,duty cycle is 50% and grating depth is 400 nm.This laser has a good wavelength selection property and narrow linewidth.The theoretical analysis conforms the numerical simulation well and it provides a good reference for the design and preparation of the device.