A testing system was established to control the liquid fuel temperature of Direct Methanol Fuel Cells(DMFCs).In view of the temperature controlling for a certain flux liquid fuel, a heating block was fabricated, in which a flexible stainless steel pipe was laid with a double-runway for heating up the methanol solution.The minimum length of the pipe and the heating power of the controlling system were calculated.Furthermore,semiconductor-refrigerating chips were utilized to heat and cool the liquid flow during testing procedures and a power actuation circuit and a transition circuit according to the controlling requirements of the semiconductor-refrigerating chips and the testing system were also developed.On the basis of PID based closed-loop controller, the liquid temperature was controlled automatically and accuratelly by a software module written in Visual C++.Experimental results show that the average cooling and heating velocity of the temperature controlling system is 14 ℃/min, and the precision of temperature controlling is better than ±2 ℃.It satisfies the system requirements of real time performance testing of DMFC.