A lawn mower with an automatic clutch has a shell, one or more blades pivotally installed in the shell, an engine in the shell for driving the blades to cut grass, a self-propelled motor in the shell, a retarding mechanism fixed with respect to the self-propelled motor, a self-propelled shaft driven by the retarding mechanism, a pair of rear wheels driven by the self-propelled shaft, a pair of front wheels on a front portion of the shell, a handle on a rear portion of the shell, a power, a control mechanism on the handle, and an automatic clutch provided between the self-propelled motor and the retarding mechanism. The automatic clutch has a tubular shell, an output shaft, a pair of symmetric block, a pair of elastic elements, an input shaft, and a crow block.
