Aiming at the problems of electromagnetic interference and shortened service life of input source caused by inherent intermittent ripple current on the input side of switching converter, a passive ripple compensation circuit for flyback converters is proposed. The circuit is composed of transformer, diode and electrolytic capacitor. Under the designed ripple suppression condition, it works in a similar flyback state and generates compensation current, which effectively suppresses the inherent intermittent ripple current on the input side. On the basis of explaining its working principle, the parameter calculation methods of system gain, suppression conditions of ripple current and related variables are deduced by using the formula. An experimental prototype with 60~80 V input, 30 V rated output voltage and 65 W rated power is built. The experimental results verify the feasibility of the proposed passive ripple compensation circuit and the correctness of theoretical analysis.