According to the absorption spectra of blood and hemoglobin, a photon-bond energy formula is established using physical methods and the effects on hemoglobin of low-level laser at different wavelengths are analyzed. The results show that lasers with the peak wavelengths of 200∼240, 275, and 342 nm in the whole blood absorption spectra curve are easy to destroy protein molecules and then lead to hemoglobin lose biological activity. While lasers with wavelengths longer than 800 nm will reduce the oxygen carrying capacity of blood, only lasers with wavelengths between 630 and 670 nm have the best efficacy.