This paper presents a method to enhance the reception performance of capacitive micromachined ultrasonic transducers (CMUTs) working in conventional mode and water immersion by adjusting the framework of vibrating membrane. The core conception of the enhancement is to reduce the system stiffness to improve both static membrane deflection under DC bias voltage and membrane displacement by harmonic analysis under acoustic pressure. Two modified structures of slotted membrane and corrugated membrane are presented respectively and the CMUT modeling is constructed and analyzed via finite element analysis (FEA) simulations by means of COMSOL Multiphysics. By using the modified membrane structures, FEA simulation shows that both the electromechanical coupling coefficient and receiving sensitivity are improved up to 20.9% and 50.5% for slotted membrane and 5.0% and 38.3% for corrugated membrane, respectively.