The invention belongs to the automation control field of a diaphragm pump, more particularly relates to an automatic fault diagnosis method for the one-way valve of the diaphragm pump, and a device which is used for the method, wherein, the diagnosis method comprises the following steps: A) when in a material feeding stroke, a sampling position is fixed and the state signal of a diaphragm room is collected; the collection value is stored and calculated; when the calculation value is larger than a set value, a material discharging valve is confirmed to be leaked; and B) when in a material discharging stroke, a sampling position is fixed and the state signal of the diaphragm room is collected; the collection value is stored and calculated; when the calculation value is larger than the set value, a material feeding valve is confirmed to be leaked. The diagnosis device comprises a switch quantity collection part, an analog quantity collection part, a relay isolation part, an isolation enlarging part, a PLC and an alarming part; when fault occurs in the one-way valve of the diaphragm pump, the device can send an alarming signal in a very short time, thus avoiding the loss caused by the fault of the one-way valve.