Based on the fundamental principle of particle gradation, the Si and CuO powder with different particle sizes were prepared. The Si-CuO delay composition with different gradation specifications was prepared. The delay precision test of various delay compositions was carried out. Results show that better granularity distribution consistency for oxidant or combustible agent is favorable for enhancing delay precision of delay composition. Third-grade particle gradation of the oxidant and combustible agent is not favorable for enhancing dely precision of delay composition. The delay composition with second-grade particle gradation, which is closer to the optimum particle gradation.