A temperature control system used in a portable computer comprises a first control part, a second control part connected to an operation processing unit (OPU), a third control part and a fourth control part connected to a charge part. The first control part outputs a first control signal for responding the temperature and load current changes of an external power transformer. The third control part outputs a second control signal for responding the temperature and load current changes of a battery. When the portable computer is powered by the external transformer, the second control part receives the first control signal to control the OPU, and the fourth control part controls the charge current of the charge part. When the portable computer is powered by the battery, the second control part receives the second control signal to control the OPU.