This paper presents a digital twin-based condition monitoring method towards power electronic converter (PEC), which can simultaneously obtain the real-time parameters of critical components including switch, capacitor and inductor. At first, a digital simulation model of PEC is built in SIMULINK/MATLAB. Then, employ Particle Swarm Optimization (PSO) algorithm to constantly update the components’ parameters in the digital model, until the simulation waveform is almost the same as that of its physical counterpart. Consequently, a digital twin imitating the actual parameter value is established for the physical PEC to realize condition monitoring. To preliminarily verify the proposed method, a simulation test on buck converter is implemented. The simulated results show that the proposed method is not only convenient, but also has high accuracy in parameter identification.