The invention discloses a charging device of a backup power source of a wind turbine generating set variable pitch system. The charging device comprises a lead-acid storage battery, a charging circuit, an electro magnetic interference (EMI) filter, an auxiliary power source, a current collecting device, a voltage collecting device, a temperature collecting device, a pulse width modulation (PWM) drive circuit and a mixed signal processor (MSP) 430 chip, wherein the current collecting device, the voltage collecting device and the temperature collecting device transmit collected signals to the MSP430 chip, the MSP430 chip transmits the signals to the PMW drive circuit, the PWM drive circuit transmits the signals to the charging circuit, the EMI filter transmits signals to the charging circuit and the auxiliary power source, and the auxiliary power source transmits the signals to the MSP430 chip. The invention further discloses a charging method of the backup power source of the wind turbine generating set variable pitch system. The charging method includes that a variable voltage and variable current wave type plus-minus zero pulse current is used, pulse current amplitude and frequency of a PWM signal are both fixed, a PWM duty ratio is adjustable, and the backup power source can be charged with more power in a short time. Accordingly, internal resistance increasing caused by long-term floating charge is prevented, and the charging device and the charging method can protect battery pole plates, and improve charging receptivity of a storage battery.