The transmitter and receiver for wireless power transfer (WPT) need information interaction to achieve optimal efficiency if the mutual inductance and load are movable. This paper proposes a receiver parameter estimation system based on the digital-twin concept aiming for condition monitoring of WPT. The digital replica and physical experimental demonstrate an application for a series-series WPT system. A hybrid optimization algorithm based on Particle Swarm Optimization and Simulated Annealing (PSO-SA) is applied to estimate mutual inductance and load based on the voltage and current of the transmitting coil from both the digital twin and the physical prototype. Compared with the conventional methods, the digital twin is real-time, without auxiliary circuits and invasion. In a validation experiment, the estimated parameters fit well with the actual values, verifying the accuracy of the proposed approach in comprehensively describing the state of the receiver. The outcomes of this study serve as a critical step for achieving noncommunication, cost-effectiveness, and power control for WPT.INDEX TERMS Digital twin, parameter monitoring, particle swarm optimization and simulated annealing (PSO-SA), wireless power transfer (WPT).