The invention belongs to the technical field of medical instruments, and particularly provides a medical infrared forehead thermometer suitable for multiple environment temperatures. The thermometer comprises a constant-temperature temperature measuring gun and a portable charging bracket, the constant-temperature temperature measuring gun comprises an upper shell, a handle is arranged on one side of the bottom of the upper shell, a temperature measuring switch is arranged at the handle, the back face of the upper shell is provided with a display screen, the front face of the upper shell is sequentially provided with an infrared transmitter and a receiver in the vertical direction, and the two sides of the upper shell are each provided with an installation cabin which is sunken inwards. By utilizing the characteristics of a cold end and a hot end of a semiconductor cold and hot sheet, a refrigerating area and a heating area which are mutually independent are arranged, air in the upper shell is circulated in the refrigerating area and the heating area through a circulating air pump, so that the internal temperature of the upper shell is controlled to be kept within the conventional working temperature range of the constant-temperature temperature measuring gun, the working temperature of the constant-temperature temperature measuring gun is expanded, and the constant-temperature temperature measuring gun can work in the environment of -10 DEG C to 45 DEG C from the conventional range of 16 DEG C to 35 DEG C.