A new type adjustable hydraulic shock absorber for a bus air suspension is designed, the solenoid valve and swing pneumatic cylinder are adopted as driving device for changing damping states. The structure and work principle of the shock absorber is introduced. By applying hydrodynamic theory, a mathematical model of shock absorber’s damping characteristic is built. Several typical algorithms for calculating damping valve plate’s deflection are analyzed. Conjugate Beam Method, an approximate method with relatively less calculation work, is chosen to calculate the deflection of valve plates. Main structural parameters’ affecting on shock absorber’s damping performance are simulated, the shock absorber specimen is manufactured. The bench test results of specimen show, “hard” and “soft” damping states switch reliably, damping force deviations between test and simulation results are less than 4%. It is verified the established model for adjustable shock absorber is correct, the Conjugate Beam Method for calculating valve plates’ deflection is effective.