A constant temperature refrigeration system for extensive temperature range application comprising a refrigerator, a low-temperature heat exchanger, a medium-temperature heat exchanger, a high-temperature heat exchanger, a pump, a first solenoid valve, a second solenoid valve, a third solenoid valve, a temperature sensor, a power regulator, a controller and a plurality of heaters, the temperature sensor is utilized for determining the working fluid temperature and compare the actual input temperature, the actual output temperature and the predetermined temperature, and the controller is utilized for switching the first solenoid valve, the second solenoid valve and the third solenoid valve for conveying the fluid to flow through various heat exchangers so that the working fluid is heated or cooled, with the result being that the working fluid temperature outputted is to reach the predetermined temperature, so as to acquire the working fluid having the exactly and precisely predetermined low temperature (-40.degree. C. to 25.degree. C.), medium temperature (25.degree. C. to 50.degree. C.) or high temperature (50.degree. C. to 100.degree. C.).