The invention relates to the technical field of power transmission, and provides a static var compensation and harmonic compensation method and a device. The device comprises a voltage and current sampling unit, a control unit and a power unit. The method comprises steps: the control unit receives voltage and current values acquired by the voltage and current sampling unit, a var compensation control quantity is acquired, and the power unit is controlled to carry out var compensation on a transmission system according to the var compensation control quantity; a positive sequence component and a negative sequence component of mth harmonic of the current value Iabc_grid are extracted; after Park transformation, proportion integral adjustment and Park inverse transformation are carried out on the positive sequence component and the negative sequence component, the control quantity of the mth harmonic is obtained; and the power unit is driven to carry out harmonic compensation according to the control quantity. According to the method, voltage and current information is firstly acquired, var compensation is carried out on the transmission system according to the voltage and current information, the positive sequence component and the negative sequence component of the mth harmonic of the current are then extracted, harmonic compensation is carried out on the harmonic according to the positive sequence component and the negative sequence component, the harmonic compensation is carried out while the var compensation is carried out, and thus the power supply efficiency is improved.