cDNA microarray is an independent platform that offers the ability to analyze large amount of data, and an important application in the organismÂ¿s metabolism and the gene expression analysis. cDNA microarray Image analysis aims to measure the intensity of each spot in the scanned image and this intensity represents the amount of a specific gene of the studied cell. The result can directly affect the subsequent analysis such as identifying different genes with different expressions. microarray image analysis includes three tasks: spot gridding, segmentation and information extraction. In this paper, mathematical morphology and spot centroid of intensity are applied to achieve an automatic way of spot segmentation. Three analysis results, including this paper, ScanAlyze software, method of Hongwei Li and method of Angulo J are compared. It shows that the arithmetic of the paper is accurate, stable and effective.