Femtocells are tiny base stations designed for the improvement of coverage and capacity of the cellular networks. Subscribers can get and install femtocells in their premises to improve the indoor signal or to increase the bandwidth when needed. However, spontaneously and arbitrarily deploying femtocells incurs difficulties of channel allocation and raises the possibility of coverage overlapping for femtocell using same channels. As a result, there will be a larger probability of co-channel interferences in the network. To mitigate the interferences among unplanned femtocells, the paper proposed an LTE femtocell coverage adjustment mechanism. Through collecting the information of user equipments (UE) and femtocells, the mechanism can determine and adaptively adjust appropriate coverage of femtocells when interferences occurred, based on signal quality, interferences and the user preference. The simulation results show that the proposed mechanism can effectively mitigate the co-channel interference. The interference rate can be reduced for 29.5% in average, and the average SINR of UEs can be increased for 212%.