Holographic waveguide could effectively decrease the weight and volume of a near-eye display system. As an important component， incouple/outcouple grating could heavily affect the final display brightness. The diffractive efficiency of a three-step grating with random duty cycle was firstly calculated and it was found that the grating with the same step width presented the highest diffractive efficiency. The simulations based on rigorous couple wave theory were exploited to analyze how grating height could affect diffractive efficiency in the case of different refractive indexes. The simulation results showed that when the refractive efficiency of the grating was 1.52 and 1.74， the grating height should be 700 nm and 470 nm to guarantee the highest diffractive efficiency. When the grating height was 100 nm less than the designed height， the diffractive efficiency decreased from 60% to 56% and from 59% to 47%， respectively. The designed grating was prepared by maskless direct-writing lithography. The measured -1 order diffractive efficiency could reach 49.7% and the output image could be clearly displayed at the end of the waveguide. The proposed three-step grating presents the merits of short preparation duty， low cost and high efficiency.