Traditional treatment of N-fossa cysts requires an incision of more than 10 cm cm in the N-fossa, the posterior side of the knee, and has a high complication and recurrence rate after surgery; modern medical advances have made us realize that N-fossa cysts are not just a cyst, but that the true cause is often a degeneration within the knee joint or an accumulation of fluid caused by the cartilage meniscus. The high pressure caused by the fluid accumulation in the joint penetrates through the fissure on the posterior aspect of the knee and forms a cyst between the semitendinosus and gastrocnemius muscles. The knee arthroscopy procedure firstly deals with the intra-articular lesion and relieves the cause of the disease and secondly eliminates the cyst quickly through internal drainage in a minimally invasive manner. The surgical incision is only 0.4 mm; it avoids complications of surgical incision, is aesthetically pleasing after surgery, and has a quick recovery. For symptomatic N-fossa cysts, the arthroscopic approach is the best choice.