Through the complex network theory, screening and dimension reduction in accordance with the TCGA(The cancer genome atlas) gastric cancer data are dealt with. We selected 275 genes related to gastric cancer, 40 samples of patients with stage IIB of gastric cancer and 36 samples of patients with stage IIIA of gastric cancer. By analyzing the gene change rate of the gastric cancer IIB sample group and the gastric cancer IIIA sample group, the joint relationship between the nodes (genes) is established. Due to the above work, the gene expression network in the process of gastric cancer deterioration is constructed. The network is analyzed by making uses of comprehensive central indicators, and 17 genes with higher comprehensive index are screened out. Using the relevant theory of complex networks to divide the gastric cancer gene network into communities, it is found that all the genes with higher index of 17 comprehensive centers fall in a large connected sub-network.This topology is consistent with the key nodes of the gastric cancer gene expression network. Therefore we have verified our conclusions on the other hand.Through comprehensive analysis, the key genes in the process of gastric cancer deterioration are obtained, which provided an effective early warning signal for gastric cancer deterioration.