In this paper, mechanical and dielectric parameters of virgin PP cellular film(t ype PQ50) were analyzed by dielectric resonance spectroscopy, and piezoelectric d33 coefficient of 18pC/N was measured. Up to 367pC/N of piezoelectric d33 coefficient for PP cellular electret was performed by means of pr essure-expansion techniques under the reasonable treatment conditions, which is about 20 times higher than that of famous ferroelectric polymer β-PVDF and whic h is higher than that of piezoelectric ceramic PZT. Based on scanning electron m icrograph and according to the piezoelectric theory model for PP cellular film t he structural and physical sources for high piezoelectric coefficient of these k inds of nonpolar porous film electret with space charge were discussed.