Abstract High aspect-ratio micro-flow channels on bipolar plates have the advantage of improving fuel cell performance. This study forms micro-flow channels with a high aspect ratio by increasing the forming pressure during the hydroforming process. This study designs and constructs a mechanical apparatus to enable a two-stage pressure increase in the hydroforming process. A high-pressure container is designed with three-layered tapered cylinders to sustain 1230.17MPa working pressures, and a special seal component is designed to seal the high-pressure fluid and maintain high pressure. The feasibility of this high-pressure hydroforming technique is verified in preliminary tests. The investigation indicates that the aspect ratio of micro-flow channels can reach 0.468 when a hydrostatic pressure of 250MPa is applied. Compared with the maximum aspect ratio of 0.31 formed using the traditional hydroforming process, the aspect ratio of micro-flow channels in this study was 51% higher, which enables the fuel cells with metallic bipolar plates to meet both performance and manufacturing requirements.