This study extracted temperature-dependent thermoelectric material parameters of thermoelectric cooler (TEC), which are indispensible in calculation of TECs performance but usually kept confidential by manufacturers. Based on the test results of a one-stage TEC and the basic thermoelectric formula, two over-determined equations were deduced by two methods of obtaining material parameters. Then two groups of material parameters were extracted by solving the two equations, and were used to calculate and experimentally verify the performance of a five-stage TEC made of the same material. Results show that the performance error provided by manufacturer became larger with the increase of the stage. The cooling temperature error of the five-stage TEC was higher than 20 K which should be noticed in the selection of the TECs. The cooling temperature error of the five-stage TEC calculated by the extracted parameters varied between 1.6~6.1 K for different cooling capacities. The calculated result of the voltage indicates that the error of the electronic resistance in the calculation model was not negligible. After modifying the voltage calculation by the extracted electrical resistance errors, the relative errors of the voltages in the working current range of TEC calculated by the two groups of parameters were lower than 4.80% and 7.00%, respectively. The maximum calculated cooling temperature error of the proposed method was about 1/5~1/2 of that by extreme value method, 1/10~1/4 of that by manufacturer. Its accuracy was comparable to the calculated result of the finite element method using the exact material parameters. This method can be used to effectively evaluate the performance of TECs with same materials.