This paper mainly introduces error calibration technology for low frequency instrument transformers test set, aiming to achieve high accuracy measurements. Firstly, the low frequency error linearity of the A/D channel in the data acquisition board is analyzed and tested. To address the low frequency error in the sampling data points, a dynamic compensation method is proposed. Additionally, the channel gain error is eliminated using the sampling sequence reconstruction method. An optimal adaptation ratio between the sampling frequency and signal frequency is designed, along with an optimization algorithm for low-frequency signal data processing, significantly improving the measurement accuracy of low-frequency instrument transformers test set. Test results demonstrate a remarkable reduction in measurement uncertainties, with ratio difference and phase difference reduced to 10ppm（10urad） for different input ratios and frequencies.