The invention relates to an inner circulating constant-temperature system comprising a temperature sensor, a signal comparing module, a signal drive module, a control module and a constant-temperature module. The temperature sensor, the signal comparing module, the signal drive module, the control module and the constant-temperature module are sequentially connected. A temperature signal generated by the temperature sensor is compared with reference voltage through the signal comparing module, a temperature value is judged, the output end of the signal comparing module controls the flow direction of currents output by the control module driven by the signal drive module, the control module outputs the currents for work of the constant-temperature module, the constant-temperature module cools or heats according to the flow direction of the currents output by the control module, and the constant-temperature module is tightly attached to a heat and cold dissipating module. The inner circulating constant-temperature system solves the problems caused by temperature, for example, an electronic product is short in service life in a high-temperature environment and can not be started and work normally in a low-temperature environment. The inner circulating constant-temperature system has the advantages of keeping a constant temperature in a sealed space of the product, prolonging service life, capable of working continuously in the high-temperature environment and preheating, being started and working in the low-temperature environment, and being good in product stability.