Low power-line is an important transmission medium to provide broadband services to end-users.In order to maximize power-line channel capacity within the limited transmission bandwidth and power,the OFDM adaptive modulation and the method of bound water injection based on the specific QoS is proposed in this paper.Set power-line channel multipath propagation model as the foundation,the closed form expression of the maximum channel capacity is given from the view of limited power of the input signal.The influence of indoor power-line channel branches number and branch length and end-load on channel capacity is analyzed. Also,in order to maximize the transmission bits of the input signals in different channel conditions,OFDM is adopted to make discretization of modulation of the input signals.The simulation result shows that the mainly factors that affect the channel capacity of indoor low power-line is line length,branch number and load impendence.In the same experimental situation,the channel capacity proposed in this paper can reach 960Mbps compared to the other methods and thus meeting the demand of high speed index in low power-line carrier communication system.