The present invention relates to a thermostatic control method for a chip and an over-temperature protecting circuit thereof, belonging to the power integrated power management IC chip field. The method converts the dissipating power generated by output current of the chip into variation of the internal temperature of the chip through a thermal resistor. Afterwards, the variation of the temperature of the chip is converted into variation of a voltage signal. After the voltage signal is amplified, the output current of the chip is controlled so that the dissipating power of the chip is adjusted and the thermostatic control of the chip is realized. The over-temperature protecting circuit is a closed loop control system formed by a temperature detecting circuit, a constant temperature amplifier and a power-to-temperature converting module. The method quantizes the entire process of 'temperature variation' of the chip by the transmission function of a continuous time domain so as to design a temperature adjusting circuit based on the closed-loop control. The method and the circuit realize that the maximization of the output power is ensured on the premise that the chip has no overheatrisk when the chip requires overheat protection.