Abstract:The 600m tunnel drilling machine is driven by hydraulic. In the working process, the hydraulic system generates a lot of heat which will be radiated by radiation system. According to heat output power, fancooled radiator was preliminarily chosen, and effective radiating area of the radiator slice was 25m2. In this paper, the function of heat change with time was derived and by the functional changes and extremum, radiator efficiency of hydraulic system was verified.