For the needs of bladder urinary volume noninvasive monitoring in clinical, we present a noninvasive bladder urinary volume monitoring system based on bio-impedance. The system uses a four-electrode structure,which is composed of a pair of excitation electrodes and a pair of measurement electrodes. The Direct Digital Frequency Synthesis (DDS) is applied to generate a 50 kHz sine current excitation source. The impedance information extracted from phase sensibility demodulation technology is transferred to a computer through Zigbee wireless technology for real-time monitoring. Two experiments are taken to verify the accuracy and feasibility of the system. The experiments results show that the system can accurately measure the corresponding electrical impedance change of the bladder. The system provides a new way to continuously and noninvasively monitor the bladder urinary volume of patients with bladder dysfunction.