The utility model relates to a constant temperature control device used for on-load freezing of a frozen soil test soil sample. The device comprises a low temperature controller (cold bath), a stainless steel cylinder, a copper pipe, two thermocouples, a data acquisition instrument, a computer, and a temperature controller, and the soil sample to be solidified is put into the stainless steel cylinder; the thermocouples are pre-embedded in central positions of the soil sample, and thermocoupler wires are led out to be connected with the data acquisition instrument and the temperature controller respectively; the temperature controller is connected with a cold bath power supply; the data acquisition instrument is connected with the computer; the cold bath is operated, a minimum temperature is adjusted, and outside circulation inlet and outlet of the cold bath are connected to both ends of the copper pipe respectively; and after the soil sample is pressurized to a target pressure through a press machine, the cold bath is started, and freezing is performed on a soil body. The constant temperature control device used for on-load freezing of the frozen soil test soil sample is simple in structure, relatively low in cost, and strong in adaptability, can rapidly and accurately control the temperature of the soil body at a target temperature, and can monitor the actual temperature of frozen soil in real time.