The basic principle and procedure of sequential Sampling inspection are discussed and the method of making the sequential sampling inspection plan equivalent to the original one is described，using the acceptance test for the density of impact point of a rocket as an example。 Four sequential sampling inspection plans, which are equiva-lent to the original one，are proposed。It is proved by Monte-Carlo simulation that the average sample quantity needed for some of the Sequential sampling inspection plans is 17%-81%less than for the original one，with variable values of standard deviation o from individual fatch of product. It has also been proved by the acceptance records of 133 batches of products from a factory during the period of four years that more than 39% of the total number of sample quantity needed for the original plan can be spared.