A sever problem that the parachute separates in advance can impede a successful rocket recovering. This paper analyzes the advanced separation and targets broken slings that function in abnormal positions under parachutes. We inspected the separation fault in field， and gleaned video and test data. Then， we conducted a simulated experiment on the parachute sling under both static tension and dynamic impact conditions， and identified the causes of the broken sling. The results inspired us to develop a scheme to prevent slings from breaking， including three measures from the perspectives of working procedure， structure and strength.