A microscopic image fusion method based on region growing judges the fuzzy degree of the microscopic image and determines the fuzzy seed block by evaluating the definition of every image block in the microscopic image. Then, the fuzzy region and clear region are exactly segmented by region growing and are marked. Finally, a clear and high-quality microscopic image, fused by a plurality of microscopic images, is obtained. Due to the combination of the definition evaluation of the microscopic image, and segmentation of the fuzzy region and clear region by region growing, the fusion results of the microscopic image of the present invention show great advantages at the subjective human perception and the objective evaluation. Furthermore, the present invention has simple calculation and stable result, is easy to be implemented and adapted for fusing the digital optical microscopic images which are shot by shallow depth of field.