A theoretical investigation to optimize thermoelectric cooling modules is performed using a novel one-dimensional analytic model. In the model the optimum current, which maximizes the COP of a thermoelectric cooling module, is determined by the cooling capacity of a thermoelement, the hot and cold side temperatures, the thermal and electrical contact resistances and the properties of thermoelectric material, but not by the length of a thermoelement. The optimum length of a thermoelement can be easily obtained using the optimum current. The effects of the thermal and electrical contact resistances, the cooling capacity of a thermoelement and the cold side temperature on the maximum COP, the optimum electric current and the optimum thermoelement length are shown.