The present invention discloses a network side device, user equipment, and a spectrum sharing method thereof. The method includes: acquiring load information of a first and a second systems; acquiring a cycle period of a shared frequency of the first and the second systems; obtaining time slice allocation information according to the load information of the first and the second system, and the cycle period, where the time slice allocation information includes a first and a second time slice; and sending the time slice allocation information to user equipment, so that the user equipment performs data transmission at the first time slice by using the first system and performs data transmission at the second time slice by using the second system and by using the shared frequency. By means of the foregoing manner, a shared frequency can be allocated, so that efficiency of transmitting system data can be effectively improved.