An improved solution algorithm of the ill-posed problem is proposed to measure the particle size distribution, which is combined with the truncated singular value decomposition(TSVD) method, the modified singular value decomposition method, the Tikhonov regularization method, and the Chahine iteration method. The singular cutoff value is determined by the Backus-Gilbert tradeoff criteria and the minimum principle of singular value. The optimal regularization parameters are determined by the L-curve method, and the simultaneous iterative reconstruction technique (SIRT) is adopted to realize the non-negative constraint of the solution. The simulation and experimental results show that the measurement errors of the single-peak and bimodal distributions are both less than 3% by the proposed algorithm. In addition, the proposed algorithm has obvious advantages superior to the other inversion algorithms in the anti-noise performance, measurement accuracy, timeliness, and measurement range of the particle size.