The photosynthetic parameters can reflect the physiological state of plants. In order to obtain a more accurate fluorescence kinetic curve, a technique for measuring plant photosynthetic parameters based on the electron transfer process was proposed in this paper. Variable excitation light pulses was employed to devide the plant photosynthesis process into two stages: fast phase and relaxation phase, and corresponding fluorescence curves were induced for each stage. The excitation bandwidth and response time were analyzed using the TINA simulation tool. The I-V conversion and MFB filter were designed and simulated quantitatively. Synchronous sampling integral technique was employed to improve the SNR of weak relaxation phase fluorescence. As a result, a complete fluorescence kinetics curve that consist of fast phase and relaxation phase was obtained, from which the plant photosynthesis parameters can be calculated using nonlinear fitting algorithm. Experiment results showed that the system SNR reached 23.8 dB, and the correlation coefficients of measured Fv/Fm that obtained by this system were respectively 0.980 and 0.997 for dark and light adaptation conditions.