Abstract: Hydraulic force increasing pulling-fishing is a new technology for fishing treatment in horizontal wells. According to the special body structure of horizontal wells and special working condition of hydraulic pressure pulling force for stuck-releasing, calculation and analysis of mechanical performance of the salvage string was conducted by using the mechanical analysis and mathematical model. This paper established the reasonable mechanical model to predict the friction losses of string and releasing force during the upward movement of strings, and then checked the string strength combining the performance parameters of hydraulic force increasing tool and the strength theory. The example analysis verified the method of model establishment and strength calibration which optimize the operation parameters of construction and laid a certain foundation for improving the safety and efficiency of relevant construction.