Due to the use of offline parameter identification methods, the existing hysteresis models are difficult to characterize the time-varying and load dependent properties from the hysteresis of pneumatic muscle (PM), which was easy to generate significant modeling errors. In order to accurately characterize the hysteresis characteristics of PM, the Prandtl-Ishlinskii (PI) model was used to describe the lengt h-pressure hysteresis characteristics of PM, and the forgetting factor recursive least squares (FFRLS) was used to identify parameters of the PI model online. Compared with offline identification, the online identification method can effectively improve the modeling accuracy of PI models. Then the feedforward online compensation controller was designed based on the PI inverse model, and a composite controller was established by combining with feedback control. This composite control approach was used to realize the motion control of PM. At the same time, corresponding experimental equipment was built and hysteresis modeling and motion control experiments of PM were conducted to compare and analyze the trajectory tracking effects of offline identification and online identification under different loads. The experimental results showed that the PI model using online parameter identification method can effectively describe the load-dependence of hysteresis and greatly reduce control errors caused by load variation.