To study the characteristics of reactive power and harmonic of Gao-Zhao high voltage direct current（HVDC） under deicing operation mode and normal operation mode， an EMTDC model of±500 kV Gao-Zhao HVDC with direct current power forth-and-reverse transmission deicing function is introduced in detail. With this model the characteristics of reactive power and harmonic at converter station are analyzed. Simulations show that:（1） Reactive power consumption at Gaopo converter station under deicing operation mode is larger than that under normal operation mode， while Zhaoqing converter station is on the contrary;（2） The amplitude of harmonic alternative current is smaller and total harmonic current distortion rate is larger compared to the normal operation mode， and the amplitude and harmonic distortion rate of alternative current voltage are both smaller than that of normal operation mode;（3） The two poles operating at different modes and the harmonic in direct system of each pole in the same converter station is different. Simulation results are helpful to the control of alternative current filter control under deicing operation mode.