This paper proposes a systematic solution for interference evaluation and spectrum coexistence of the integrated satellite-terrestrial communication system, which can be used to evaluate interference and analyze spectrum coexistence quickly and effectively. With this solution, we evaluated the interference of the international mobile telecommunication (IMT) system to the satellite downlink in the 24.25–27.5GHz band. In addition, we studied the interference of the IMT base station (BS) electronic down-tilt angle and network load factor (NLF) on the satellite downlink. Specifically, we compared the interference received by the satellite earth station under different electronic down-tilt angles, as well as the interference of the fluctuating NLF and the fixed NLF on the satellite downlink. The simulation results show that the spectrum coexistence in the satellite-terrestrial communication system can be realized by setting the NLF, the electronic down-tilt angle, and the isolation distance reasonably. This solution is conducive to the research on the spectrum coexistence of the satellite-terrestrial communication system.