A multi-constraint payload releasing criterion approach to four flight conditions is proposed to ensure that the flight parameters of a sounding rocket enter the specified release envelope. The straight line shifted by the left boundary of payload release envelope and backup time is used as the determination condition of load releasing, and the relevant parameters are reasonably designed. The criterion approach was verified by numerical simulation of Monte-Carlo and four flight tests of sounding rocket. The results show that the criterion approach can make the flight parameters at the load release point fall into the specified envelope in each flight test, which is simple, reliable, inclusive and of important engineering value.