In order to improve the transmission rate of broadband Power Line Communication (PLC), a dynamic subcarrier allocation algorithm based on rate maximization (RA) principle is proposed under the condition of low-voltage broadband power line channel in 2~100 MHz. The algorithm exploits the better global search–capability of genetic algorithm and combines the genetic algorithm and water injection algorithm to adaptively allocate subcarriers of Orthogonal Frequency Division Multiplexing (OFDM) system. In the new algorithm, it first cross-operates the individuals in the population to obtain two new progeny populations, and reproduces and mutates the obtained progeny populations. Compared with the adaptive genetic algorithm, simulation results show that the whole PLC system performance is improved, the system transmission rate is faster, and the channel capacity becomes larger. This work is supported by Science and Technology Project of Hebei Province (No. 17211704D) and Fundamental Research Funds for the Central Universities (No. 2018MS096).