Based on the knee MRI, the degree of ACL injury can be determined and is divided into three levels. Grade I ACL signal has damage, but the ACL integrity is good, and stripes and lamellar high signal are visible within; Grade II is ACL signal has damage, part of the ACL signal integrity is interrupted, high signal appears, the range does not reach the joint surface, and a small amount of surrounding fluid accumulation; Grade III is ACL signal has damage, and the ACL is completely broken, out of the surface obviously high signal, linear high signal reaches the the articular surface.