The component parameters of the circuit significantly affect the control performance of Buck converters, especially the inductance and capacitance. A reference voltage pulse injection method is proposed for the online estimation of inductance and capacitance. The full-rank state equation is constructed using the original steady state and the new steady state to improve the estimation accuracy of inductance and capacitance in the Buck converter. The parasitic parameters and load resistance required by the algorithm are derived online. The precise discrete-time converter model based on the volt-second characteristic of the inductor and the charge balance characteristic of the capacitor is studied, which lays the foundation for parameter estimation. A short pulse signal is injected into the reference voltage, and using a PID controller to regulate the inductor current and output voltage in the circuit, a transient state and a new steady state for parameter estimation are established. The inductance and capacitance values are estimated using the voltage and inductor current sampled in the transient state, which avoids the convergence problem in the steady state. Based on the proposed average inductor current estimation algorithm, the current sampling frequency is reduced to the switching frequency. Finally, the simulation verification is carried out on Matlab/Simulink platform, and the results show that the maximum estimation errors of the inductor and capacitor values are less than 2% and 4.2%, respectively, even when considering the actual noise. Compared with other parameter estimation algorithms, the introduction of the reference voltage pulse injection method can effectively improve the estimation accuracy of parameter identification and contribute to the improvement of the control performance of the Buck converter system.