Abstract: The propellant injection for spacecraft at the launch site is the most dangerous procedure in the whole R&D process, which involves many dangerous operations. Strict protective measures must be taken to avoid any mistakes. Based on the experience of previous practices, and by adequate design and discussion aimed at improving the current hardware conditions, the operation procedures for propellant injection of spacecrafts are optimized with a great enhancement of the intrinsic safety. These approaches have been applied in China's first rendezvous and docking mission, which brings about successful accomplishment of the propellant injection of the Tiangong-I and Shenzhou-VIII spacecraft.