Based on the experimental data of same batch 80 samples before irradiation, and after 100, 200, 500, 1 000, 1 500 Gy total dose irradiation, the statistical law of a domestic operational amplifier LM124 under total dose irradiation was analyzed. A logarithmic normal distribution characteristics of input bias current variation was found, and the median input bias current changed within 3.6~7 nA linearly under irradiation. Also, the variation increased simultaneously with total dose. A positive linear correlation between the radiation damage and the initial value was obtained with the calculation method of the parameters. The linear coefficient (α) of the five total dose points from 100 to 1 500 Gy was 0.24, 0.31, 0.5, 0.77 and 1.07, respectively, and α showed a linear increment with the total dose. The mechanism of initial value dependence was physically explained, that is, the quality of oxide layer above EB junction determined the total dose irradiation response of the device (initial value dependence). The research results could effectively support the quantitative evaluation of radiation reliability for circuit or system based on LM124, and had a reference value for the total dose effect reinforcement screening of bipolar devices.