Abstract: By the analysis of automated tape laying (ATL) process, the viscosity-temperature relationship of the composite prepregs was investigated. By the research on hot-air temperature and placement rate, which are two main factors on the prepregs temperature, the theoretic relationship between hot-air temperature and placement rate was examined, and then the controlling method of prepregs temperature was proposed to guide the ATL manufacturing. Finally, according to the viscosity-temperature curve of the bismaleimide resin prepregs, the experiments were conducted under different hot-air temperatures and placement rates. The results show that the viscosity of the prepregs agrees with the processing demand when the hot-air temperature is set at 90℃ and the placement rate is about 10-20m/min. The research work indicates the influence on the composites structure, caused by prepregs hot-air temperature and placement rate, which will be helpful for the ATL process.