In order to ensure the accuracy and reliability of terahertz radiation intensity measurement, the responsivity calibration of pyroelectric terahertz detectors is carried out. First, a terahertz detector responsivity calibration device is constructed based on the substitution method, and the combined standard uncertainty of the device is 2.4%. Then, the 12D-3S-VP type terahertz detector is calibrated by the calibration device at the frequency point of 1.63 THz, and the responsivity calibration result is 197.6 mV/W, which is consistent with the value given by the manufacturer. The self-developed pyroelectric terahertz detector is calibrated, and the responsivity and the combined standard measurement uncertainty are 362.2 mV/W and 2.7% respectively. Finally, the standard deviation of the calibration result is compared with the combined standard uncertainty, and it is found that the standard deviation is in a reasonable range, which further proves the rationality of the calibration method, calibration results and uncertainty analysis.