To address the need for real-time data interaction in precision wireless power transfer systems and the problem of multi-channel interference, this paper proposes a simultaneous wireless power and data transfer (SWPDT) system based on dual modulation bidirectional transmission using Differential Phase Shift Keying (DPSK) and Amplitude Shift Keying (ASK). First, the system adopts a frequency-domain orthogonal isolation structure: the power channel is fixed at a fundamental frequency of 85 kHz, the DPSK signal is allocated a 4 MHz carrier for forward transmission of control commands from the primary side, and the ASK signal is allocated a 1.5 MHz carrier for reverse transmission of status feedback from the secondary side. Combined with a double-sided Inductor-Capacitor-Capacitor (LCC) compensation topology, it achieves constant current output on the primary side, ensuring reliable and stable power transfer. Then, impedance analysis and the frequency-domain orthogonality theorem are used to verify that the signal and power channels do not overlap in the frequency domain, effectively reducing crosstalk. Finally, simulation results demonstrate that the system can maintain stable 85 kHz power transmission while achieving full-duplex data communication.