Hydraulic systems are popular on vehicles, such as power steering, shock absorbers, brakes, etc. Many previously works have been done on the modeling and simulation of the hydraulic systems. However, these models and parameters are usually established on the basis of plans, drawings, measurements, observations, experiences, expert knowledge and standards, and so on. In general, certain information and precise values do not exist. Uncertainty may result, e.g., from human mistakes and errors in the manufacture, from the use and maintenance of constructions, from expert evaluations, and from a lack of information. Actually, many uncertain factors will lead to great errors, and may have great effect on the hydraulic system, so the research on the hydraulic system under uncertainties is very necessary. In this paper, fuzzy algorithm is introduced to analysis the response of the hydraulic system with uncertain parameters. By using fuzzy set theory, uncertain input parameters such as the source pressure, the stiffness of the return spring, the friction between the piston and the chamber, etc., are described mathematically as fuzzy variables or fuzzy random variables and integrated into hydraulic system analysis. The simulations are carried out to analysis the system performance under fuzzy uncertain parameters. Results are presented showing the effectiveness of the method for modeling systems with uncertain parameters.