According to the thickness and the pre-deformation of throttle slice, and the throttle hole area, the velocity points of valve opening were analyzed by the relation of flux to the velocity, and pressure to the deformation of throttle slice, then the analytic formulas of telescopic damper velocity at which valve opening were given. The outer characteristic model of telescopic damper was established by piecewise linear function. A practical example of simulation of telescopic damper outer characteristic was given, and the performance test was conducted. The results show that the model of outer simulation is correct, and the simulation values coincide with test values.