The response of a commercial thermopile TPS434 to IR light as a function of temperature between 280 and 10 K, chopper frequency between 0.1 and 100 Hz, and magnetic field between 0 and 6T was measured in order to investigate its suitability for THz detection. The data show that the sensitivity of TPS434 decreases with the decrease in temperature or the increase in chopper frequency. The relaxation time of TPS434 at low temperature is smaller than that at room temperature, which can improve the system response time. Thermopile’s thermoelectromotive force increases linearly under low temperature with the magnetic field increasing, but the influence of the magnetic field can be deducted through the linear fitting to the measurement result. The possibility of using the device as a THz detector was analyzed by estimating the equivalent noise power (NEP) and the smallest detected power Pmin.