The invention relates to a biochemical instrument, and provides a constant temperature metal bath, which comprises a base, a warming and cooling part and a radiating part, and also comprises a heat-conducting fin used for heat exchange, wherein the upper and lower surfaces of the heat-conducting fin are attached to the base and the warming and cooling part; and the coefficient of heat conduction K of the heat-conducting fin is more than 237W/m.K. A layer of heat-conducting fin is arranged between the base and the warming and cooling part, and thermal interface materials are coated on contact surfaces among the base, the heat-conducing fin, the warming and cooling part and the radiating part, and the heat conducting uniformity is enhanced; a thermal insulation gasket is arranged between the base and the heat-conducing fin, and the thermal insulation function of the base is enhanced; an exhaust fan is moved to the bottom, and the number of the exhaust fans is increased, so that the warming and cooling efficiency is improved; and an anti-condensation device and a gasket are arranged above the base, and a lantern ring is arranged at the periphery of the base, so that the usability of the constant temperature metal bath is improved.