The present invention relates to a PWM isolation dimming circuit and an LED dimming driving power source, wherein the PWM isolation dimming circuit comprises: a square-wave generator circuit, used to generate a square-wave signal by oscillation; an integrating circuit, wherein an input end thereof is connected to an output end of the square-wave generator circuit, and the integrating circuit is used to perform an integral operation on the square-wave signal, to generate a triangle-wave signal; a PWM generator circuit, wherein an input end thereof is connected to an input end of a dimming signal and an output end of the integrating circuit, and the PWM generator circuit is used to compare the dimming signal with the triangle-wave signal, generate a PWM signal according to a comparison result, adjust a duty ratio of the PWM signal and output an adjusted PWM signal; and a photocoupling circuit, wherein an input end thereof is connected to an output end of the PWM generator circuit, and an output end thereof is connected to a control end of an LED driving power source, to control an output current of the driving power source. The foregoing PWM isolation dimming circuit and LED dimming driving power source have advantages of being good in degree of linearity, small in circuit volume, and low in costs because a high-frequency transformer is unnecessary.