In order to improve the precision control of the duty cycle and the groove depth of a recorded profile in the photoresist, based on the nonlinearity of the photoresist in development processing, a binary resist mathematical model for simulating the profile evolution of the photoresist grating is presented, according to this model, the changing of the profile characteristics such as duty cycle and the groove depth which depend on the contrast and exposure dose can easily be understanded. It turns out that: under specific development condition and the exposure upper limit Ec recognized by calculating and experiment, the duty cycle of the grating masks decreases as the exposure dose increases, the decrease of fringe contrast not only results in the decrease of the duty cycle, but also results in the decrease of the groove depth. The model can show the profile evolution trend exactly, it provides a right analysis tool for forecasting and controlling the groove shape in the fabrication of the grating masks.