The infrared image quality and temperature resolution is degraded significantly by the non-uniformity response of infrared focal pattern array. Calibration-based and scene-based non-uniformity correction algorithms provide feasible way to handle this problem. Due to its simplicity and accuracy, traditional blackbody calibration-based non-uniformity correction method is widely used but with the disadvantage of highly dependence on the existence of blackbody and its temperature control equipment to provide uniform irradiances. In this paper, an improved two-level non-uniformity correction algorithm based on integration time calibration was proposed. Given the irradiance, the different response data is first obtained through integration time variation. Then the least square method is used to estimate the initial gain coefficients and bias coefficients for two point correction algorithm. Finally, the one point correction coefficients are estimated throuth two point correction of different response data. Experimental results show that the proposed algorithm has the merits of low complexity, high precision, excellent non-uniformity correction performance, and can easily be integrated into hardware platform.