Image reconstruction algorithm is the key to the industrial application of electrical capacitance tomography. The Landweber iterative algorithm has achieved a good compromise in the accuracy and speed of image reconstruction, but its convergence speed is slow, and the late iteration is unstable, there is no clear iteration stop criterion. In this paper, an improved gradient accelerated Landweber iterative algorithm is proposed, based on the series theory, the gradient accelerated Landweber iterative algorithm is deeply analyzed, a new iterative formula is obtained by constructing the residual matrix and adding constraint factors, and it is applied to ECT Image reconstruction. Numerical simulation results show that the relative error and correlation coefficient of the improved algorithm can converge to a certain value after less iteration steps, and has a clear iteration stop criterion. Moreover, for most flow patterns, the reconstructed images are closer to the original flow patterns in subjective quality, which verifies the stability and effectiveness of the improved algorithm.