Abstract: Microelectromechanical system (MEMS) pressure sensors offer advantages such as compact size, fast response, and ease of integration, and are widely used for pressure monitoring in aerospace, power equipment, and industrial processes. However, in conventional silicon piezoresistive pressure sensors, the diaphragm typically serves both load-bearing and sensing functions, making it difficult to balance structural strength and strain output under high pressure. To address these challenges, we propose an inverted graphene piezoresistive high-pressure sensor with functionally separated load-bearing, force-transmission, and sensing components. The structure employs a steel diaphragm for pressure loading, a central post for force transmission, and silicon beams for strain sensing. Finite-element analysis is used to optimize the dimensions of the steel diaphragm and beams, evaluate the pressure response over 0–20 MPa, assess unprestressed modal characteristics and interference induced by z-direction equivalent static acceleration loads, and establish a theoretical quarter-bridge model under ideal strain transfer with a graphene gauge factor (K) of 2. The results demonstrate a strain sensitivity of 1.3376×10⁻⁴ MPa⁻¹, a coefficient of determination of 0.99993 for the pressure-strain fit, and a first unprestressed natural frequency of 198.80 kHz, which serves as a reference for the resonance-frequency margin. Additionally, the theoretical normalized output is 1.34×10⁻³ at 20 MPa. Under a non-resonant z-direction equivalent static acceleration load of 500 g, the maximum equivalent stress in the steel diaphragm is 0.729 MPa, the additional normal strain in the sensing region is 1.935×10⁻⁶, and the equivalent pressure error is 0.072% of full scale (FS). By separating the load-bearing, force-transmission, and sensing functions, the proposed structure provides a reference for designing pressure sensors intended for high-pressure and high-acceleration environments.