It was studied systematically by 3130XL genetic analyzer for the effects of ninhydrin development of latent blood fingerprint on white paper on the subsequent DNAshort tandem repeat(STR) fluorescence pattern. Results show that the DNA detection efficiency decreases for the latent blood fingerprint developed with ninhydrin compared with control group without being developed. The detected number of STRs is gradually reduced with the concentration diluted about the latent blood fingerprint developed with ninhydrin. It is of great significance with this paper to the extraction of evidence at the crime scence.