The effects of DNA-short tandem repeat (STR) profiling about latent blood fingerprints on different surfaces are studied by 3131XL genetic analyzer which are irradiated by ultraviolet light. Results show that the DNA of latent blood fingerprints on porous surfaces is damaged worse than that on non-porous surfaces after ultraviolet irradiation. In the same amount of time of ultraviolet irradiation, with the concentration of the dilution, the detected number of STRs is gradually reduced.