A design of wireless signal strength measurement system in real time by using GNU Radio and USRP(Universal Software Radio Peripheral) is proposed in this paper . To quickly and accurately measure the signal strength, this paper use the band noise power, spectral filtering and moving average techniques in the frequency domain in the signal receiver. The system is lowcost, flexibility, scalability and portability, thus could reduce the system maintenance as well as upgrade costs. Finally, in the indoor wireless environment, measured the intensity of the filed compared the measured data with the raytracing simulation data the result proves the feasibility and effectiveness of the system in a real environment.