Abstract: An on-line automatic cleaning apparatus of slit extrusion type coating die for lithium battery and a method associated therewith are provided. The cleaning apparatus includes: a die lip, a coating steel roller, and a cleaning mechanism disposed therebetween. The cleaning mechanism includes a cleaning chamber which includes elongated sealing strips and a flow-guiding arc groove. Front and rear ends of the cleaning chamber are connected to an inlet sealing plate and an outlet sealing plate respectively. The flow-guiding arc groove is in contact with and presses upper and lower sloped surfaces of the die lip through the elongated sealing strips to seal and thereby define a closed cleaning tunnel. The inlet and outlet sealing plates are in contact with and press two ends of the closed cleaning tunnel respectively for circumferential sealing. An inlet and an outlet are connected to pipes having solenoid valves installed thereon.