The invention discloses a monitoring device with a camera lens protection film capable of being automatically pasted and replaced and a film pasting method of the monitoring device. The monitoring device comprises a device body and a monitoring camera lens arranged at the bottom of the device body. First slide grooves are formed in the two sides of the monitoring camera lens correspondingly and located in the device body. The two first slide grooves are symmetrically formed. First slide rods are installed in the first slide grooves in a sliding manner. A film replacement head is arranged at the end, close to the opening of the corresponding first slide groove, of each first slide rod. First containing cavities are formed in the two sides of the device body correspondingly. First drive motors are arranged in the first containing cavities. Output shafts of the first drive motors are connected with fixing columns. The two fixing columns are located on the two sides of the device body correspondingly. Second slide grooves are formed in the fixing columns. By means of the monitoring device and the film pasting method, the camera lens protection film can be automatically pasted and replaced, the automation degree is high, it is avoided that monitoring pictures are fuzzy after long-time use and consequently the monitoring effect is influenced, the structure is simple, use is convenient, and cost is low.