Objective To explore the source of endothelial cells in tumor vessels by A 549 tumor model with GFP nude mouse.Methods To establish the A 549 lung cancer models with GFP nude mice, expression of CD 31 was determined by immunofluorescence to label tumor vessels; to observe and take a picture of the tumor frozen section by confocal microscopy and invert microscope; expression of GFP in tumor vessels was determined by immunohistochemistry. Result The results of immunofluorescence showed: Tumor interstitial vascular endothelial cells or endothelial cells clusters and micro-vascular lumen size and shape are clearly visible by immunofluorescence, and part of vessels with no obvious lumen or irregular lumen. We can see green fluorescent in tumor cells of tumor tissue and endothelial cells which form of tumor vessels. The results of immunohistochemistry showed: expression of GFP was determined in cytoplasm of tumor stromal cells and endothelial cells in tumor vessels. Conclusion The endothelial cells which formed tumor neovessels that derived from GFP nude mice partly and the other part derived from tumor cells.