During the past decade, a growing attention has been paid to the Lamb waves propagating in composite plates due to a variety of applications for nondestructive evaluation, vibration attenuation and Lamb wave sensors. We present a revised plane wave expansion method and a finite element method to study the large partial band-gaps of a multiple Lamb wave phononic crystal thin plate with a symmetric mirror plane The results show that lots of partial stopbands of lower-order Lamb waves exist and can be substantially enlarged by using multiple heterostructures which consist of several pieces of phononic crystal with different ratios of the thickness (H) to the lattice period (L). These contribute to good mode choice for lower-order Lamb waves, which is believed to have much significance for optimially choosing models in Lamb wave nondestructive test and the one-way Lamb wave mode transmission.