The researches about the LOX/LCH₄ expander cycle throttling liquid rocket engine are rare and its recognition of it is not distinct, especially at the system level. Based on the whole engine system, the theoretical method was adopted to investigate the work capacity of CH₄ and the feasibility of throttling schemes. The single-turbine and double-turbine throttling schemes were given, and the detailed comparison between them was analyzed. The results reveal that CH₄ work capacity decreases at first and then increases with the decrease of chamber pressure. And the proposed throttling schemes are feasible. Moreover, compared with the single-turbine scheme, the oxidizer and fuel mass flows can be adjusted respectively for double-turbine scheme and the mixture ratio can keep constant better. Meanwhile, the work capacity of CH₄ for double-turbine scheme is much higher, the powers of the oxygen and fuel turbines vary in a narrow range, and the turbines work in a more relaxed environment. Therefore, considering the system reliability, the double-turbine scheme is advantageous to a certain extent.