Hypervelocity impact can produce instantaneous plasma during the impact． Through two kind of sensor designed in this paper to collect the plasma to attain the arriving time of the particle, we use the time of flight method to obtain the velocity of the particle． During the elementary experiment in the plasma drag particle accelerator, the impact signal was captured and the measurement of the particle velocity was achieved．The experiment result proves that this method has a high precision in time survey and a high signal to noise ratio．