The invention relates to a circuit for realizing automatic color gradient of an RGB three-primary-color LED lamp. The circuit is simple to realize and low in power consumption is low; in the implementation process, a main control chip only needs to write a register for the circuit to set the initial color, the target color and the gradual change duration and enables a color gradual change function, and the circuit can carry out calculation automatically and realizes automatic, linear and fine color gradual change effects according to setting without occupying resources of the main control chip(MCU) for a long time, so that the power consumption of the system is greatly reduced; and moreover, the color gradient circuit can be integrated in an LED driving chip, so that the difficulty of system-level lamp effect design is greatly reduced.