Aiming at the problem that the power supply stability of coal mine grid is affected by harmonics and load imbalance, an active filter optimisation algorithm based on the hypercomplex algebraic algorithm is proposed to strengthen the adaptability of the instantaneous power decomposition with the compensation control of Active Power Filter (APF). The harmonic characteristics of the three-phase system are analysed and optimised by combining the instantaneous active power and reactive power theories and introducing the vector algebra algorithm. (THD)xperimental results show that the Total Harmonic Distortion(THD)value of harmonic voltage is lowered from 9.52%to 1.82%. The algorithm not only reduces the harmonic content of the coal mine power grid, but also provides an important optimisation algorithm and practical reference for the stable operation of the mine power supply system.