Abstract: The power supply system of heavy ion accelerator requires high stability and ripple precision of excitation power supply. Because of the existence of magnet load, the ripple has an impact on the precise control of particle trajectory by magnetic field. To solve the above problems, a new combined algorithm based on SSOGI-RLSMC is proposed to reduce the output current ripple of excitation power supply under the influence of magnet load and improve the current stability. The new joint algorithm extracts the ripple component quickly and accurately by using the parallel Second-Order Generalized Integrator(SSOGI) as the ripple detector, and obtains the command current with high precision. The error signal is obtained by subtracting the command current and the compensation current of the DC active power filter, and the Reaching Law Sliding Mode Control(RLSMC) algorithm is used to track and compensate the error signal dynamically, so as to improve the direct current active power filter can suppress the ripple of the output current of the excitation power supply, so as to achieve the precise control of the particle trajectory. Finally, through MATLAB/Simulink simulation, it is proved that the new joint algorithm can effectively improve the accuracy and stability of the output current of the excitation power supply, and improve the ripple current suppression ability of the DC active power filter.