Abstract: Viscous heating of valve orifice not only wastes energy but also causes thermal deformation． It increases the risk of spool clamping and exerts a strong impact on the stability and safety of hydraulic machines． A deep research on the temperature distribution of valve orifice is the foundation of accuracy prediction of thermal deformation，so a temperature measurement method was put forward by embedding miniature thermocouples in different locations of the planar valve orifice． The experiments were conducted with the valve opening x ranges from 1 mm to 3 mm and inlet pressure pin ranges from 0. 5MPa to 3MPa． The results show that the valve orifice temperature rises with the increase of the inlet pressure; the heating rate can reach 0. 79 ℃ /min when x = 2 mm and pin = 3. 0 MPa; the temperature of valve orifice caused by viscous heating distributes unevenly，and the temperature gradient seems more sensitive to pressure drop under a small orifice． The maximum temperature difference of valve orifice can reach 7. 86 ℃ when x = 1 mm and pin = 3. 0MPa． In most cases，the sharp edge of the valve orifice is likely to generate a higher temperature，which can reach 72. 9 ℃ after heating 110 min under 3. 0 MPa． However，a higher temperature will also appear along the vertical edge under a larger valve opening or a higher pressure drop． To analyze the phenomenon，a comprehensive analysis was carried out by combining fluid-solid-heat coupling module and mixture multiphase flow model in ANSYS Fluent software． The results show that the vortex and cavitation have a strong impact on the temperature distribution in the wall of the valve orifice．

Key words: hydraulic valve orifice, viscous heating, miniature thermocouple, temperature distribution, numerical analysis