Terahertz photothermoelectric detectors are based on the principle of thermogenerated carriers migrating under the influence of a temperature gradient to achieve terahertz wave detection. They have advantages such as fast response, ultra-wideband, self-powered, room temperature operation, and simple structure, which have attracted widespread attention. Currently, the readout of detectors mainly adopts a modulation-demodulation method, realized by cascading a current amplifier with a lockin amplifier for measurement, which has low integration, high cost, and is difficult to achieve array readout. To meet the application requirements of spectral measurement and imaging perception, this paper studies the readout method of the photothermoelectric array detector unit. Starting from the detector mechanism, the output signal is modeled and analyzed; based on this, a board-level dedicated readout circuit is designed to achieve front-end amplification and lock-in amplification functions. Tests show that this method can achieve high-precision readout of terahertz photothermoelectric detectors in a strong noise background environment, with a gain of 140.7 dB, and the signal-to-noise ratio is improved by 38.3 dB.