Based on the extended scalar diffraction theory （ESDT）， the theoretical model of the relationship between the microstructure height， the period width and the incidence angle of diffractive optical element（DOE）was established. The optimal design method of the structure parameters， such as design wavelength and microstructure height， was proposed based on the maximization of the bandwidth integral average diffraction efficiency （BIADE） at different incident angles. A DOE working within the near infrared waveband was taken as an example. Results indicated that when the period width was determined， the change of incident angle could cause the change of structure parameters obtained based on the maximization of BIADE. The designed method and conclusions could be used to guide the design of DOE.