Range alignment is a key procedure in ISAR (Inverse Synthetic Aperture Radar) imaging. Based on the study of the global minimum entropy range alignment algorithm, an improved range alignment algorithm is put forward according to the subinteger range-bin method and through the analysis on the influence of correlation between echoes on the original algorithm. Range profile blocking scheme and subinteger range-bin alignment method are applied on the presented algorithm. Range profile blocking scheme and subinteger range-bin alignment method improves the accuracy and precision of the original algorithm respectively. The real data processing result shows that this algorithm improves the accuracy of range alignment and hence improves the ISAR imaging quality.