The accuracy of non-invasive detection devices using photoplethysmography signal (PPG) for blood content often fails to meet the medical clinical standards. The reason for the error is partly due to theoretical algorithms, and partly due to the design of hardware. PPG signal acquisition device puts pressure on the skin during measurement, which affects the PPG signal. Aiming at this problem, this paper uses the finite element method to construct a skin model under pressure, and the optical transmission simulation experiment are used to analyze the changing trend of the reflected light intensity under different pressures. It was found that the change of reflected light intensity with pressure is related to the detection distance and wavelength. Simultaneously, the PPG sensor in our laboratory are used to carry out pressure experiments. The measured results verify simulation results. The influence of pressure on the DC, AC component and quality of PPG signals are analyzed ulteriorly. And we found the optimal pressure range is 0.4N~1.2N for 7 subjects.