To mitigate the negative impact of modular multilevel converter （MMC） based high voltage direct current （HVDC） systems partitioning on frequency stability, a method for frequency coupling control of the sending and receiving ends is proposed, and the system stability after adopting this method is analyzed. Firstly, for the receiving-end MMC station, a coupling additional control of DC voltage and AC frequency is proposed, mapping changes in AC frequency to the DC voltage signal. Secondly, for the sending-end MMC station, active power additional control is proposed, adjusting the reference value based on changes in sending-end frequency and DC voltage. Then, under the application of the aforementioned control method, a state-space model of the AC/DC system is established to analyze the impact of frequency coupling control on system stability. Finally, tests are conducted in a modified IEEE 11-bus system to validate the effectiveness of the proposed frequency coupling control method and the correctness of stability analysis results.