We present a piezoelectric micromachined ultrasonic transducers (pMUTs) with center support membrane. A finite element model has been created in COMSOL Multiphysics. Its vibration membrane is connected with other structures only through the central support column or wall. Since the outer edge of the membrane is not clamped, the membrane can have large vibration amplitude. Compared with the traditional clamped pMUTs, this center support structure has a larger average vibration amplitude and higher electromechanical coupling coefficient. According to the simulation results, the pMUTs with center support have an order of magnitude larger average vibration amplitude than traditional pMUTs with clamped circular and rectangular membranes. Besides, their electromechanical coupling factor k2t are 0.5808% and 0.4185%, which is also ahead of the traditional ones. The structure proposed in this paper has significant advantages in ultrasound emission and energy conversion efficiency, and is conducive to various airborne applications.