The invention discloses an experimental method using cellulose acetate film replication to acquire fatigue small crack condition of sheet metal and relates to the field of mechanical structure fatigue. The experimental method includes: during front-back replication, adopting a big hairbrush for quick brushing to enable a film to be pasted on the sheet metal at a time, and using a small hairbrush to dip acetone to remove bubbles from left to right, wherein the moving direction of the hairbrush is perpendicular to a load bearing direction of the sheet metal, and the moving direction of the hairbrush and the surface of the sheet metal form 20 degrees; during replication of the side face of the sheet metal, adopting the small hairbrush to dip acetone, enabling the hairbrush to contact with thesheet metal above the film to enable the acetone to flow down the film and to enable the film to be pasted on the side face of the sheet metal, and pressing the hairbrush to squeeze out the bubbles in the film; during extracting of the film from the front and the back, using a finger to poke the film exposed on the outer side repeatedly to enable the film to slowly expand; during extracting of the film from the side face, using the hairbrush to slightly brush to enable the film to warp up, and using a finger to poke the film exposed on the outer side repeatedly to enable the film to expand. By using the experimental method, replication success rate is increased, and experimental accuracy is improved.