The physical mechanism of green laser inducing erythrocyte fluorescence spectra in vitro is analyzed by a model of non syntonic dipole in this paper. The theoretical investigation shows that while the erythrocyte from blood is radiated by a low lever frequency doubled Nd∶YAG laser with wavelength 532 nm, anisomerous C-C bonds or C-N bonds on membrane of the erythrocyte would absorb the energy by non resonance and be parted to produce lone pairs of electrons. The new fluorophores from the lone pairs of electrons under the laser excitation would emit fluorescence. It may supply some references to the explanation the mechanism of low level laser irradiating blood therapy in vivo.