This paper presents an underwater wireless power and data transfer (WPDT) system with the shared channel. The power and signal could be transferred with the same channel based on the time division multiplexing theory. In one switching cycle, the power is transferred in the first half switching cycle and the signal is transferred in the second half switching cycle. The signal is modulated with the frequency-shift keying (FSK) method. The frequency for the power delivery is set as 240 kHz. With the FSK modulation method, the frequencies of two carriers are set as 10 MHz and 2 MHz for signal transmission, respectively. The glass tank experimental platform is constructed with the 35‰ salinity water. The simulated and experimental results verify the theory analysis and the calculation very well.