Femtocell is a sort of miniature mobile base station system in order to adapt to the development of 3G mobile communication system. It shares the spectrum resources with the operators’ other mobile base stations by cognitive radio spectrum sensing. As the power controlling technology is applied to 3G systems, the sensing performance of traditional energy detection is affected. In order to solve the problem, a cooperative spectrum sensing is proposed according to the characteristic of Femtocell system. It fuses energy detection spectrum sensing and timing advance detection spectrum sensing. The analysis and simulation results show that this method can narrow the false alarm range of Femtocell system under the same sensing accuracy. Thus, the utilization of spectrum resources can be improved.