Adjustable linear hydraulic dampers are widely used in high-speed trains to improve their ride comfort and stability, the distinctive damping characteristics of the dampers are intrinsically predetermined by their inner complete valve systems. Therefore, design of the complete valve system parameters for each damper type is of crucial importance. A multi-objective design optimization model for the concept of optimizing both the technical and economic capabilities of a three-valve complete valve system in a hydraulic damper was formulated, based on full damper dynamics modelling. A linear weighted criterion method was used to transform the established multi-objective problem to a single-objective problem, and a computer package employing the genetic algorithm for the optimization search was developed. Implementation of the design optimization was performed, and an optimal result, with about 10.29 per cent improvement of the overall fitness value, was obtained. Simulation results show that the optimal result satisfies all the competing objectives well within the constraints, except for some minor and tolerable tradeoffs in the relief valve response performance. Prototype experiments validated that the prototype dampers have obtained excellent damping characteristics, as expected. Thus, the complete valve system of the hydraulic damper was comprehensively optimized, with respect to both the technical and economic concerns. The approach developed in this work has already been applied to the engineering design of several hydraulic damper products in industry.