A tortuous labyrinth passage consists of a series of right angle ts in a disk of high pressure control valve. In this paper, numerical simulations are made for the velocity and pressure distributions in this passage. It is shown that the “series passage” can induce a pressure dropping more effectively. The main function of the “series passage” is to induce a pressure dropping while the “parallel passage” is mainly to regulate the flow-rate. As a cross sectional area process, a series of reduction and expansion, the pressure will also see dropping and partial recovery, which is called the multistage pressure drop. By this way, the velocity can be controlled in a reasonable level anywhere in this tortuous labyrinth passage. With the fluid pressure dropping in a downwards serrated way, the pressure is higher than the local saturate vapor pressure, therefore, no cavitation is induced by the phase transition.