Under the conditions of downhole closure in oil well, the wired transmission of the data signal including downhole temperature and pressure cannot be achieved. To solve this problem, an experimental study of short distance wireless system for downhole data transmission was launched. This technology is based on the means of electromagnetic coupling to achieve the wireless transmission of signals by leaps and bounds. Through the test bench of the wireless electromagnetic short pass system, we carry out the frequency characteristics of the transmission channel experiments, and provide the foundation for the design of downhole power supply lines and the selection of the electronic components. The tests show that the output characteristics of the downhole wireless signal transmission system are stable. They did not change with the excitation voltage, and the transmission frequency band between 50-100 KHz is better.