A model of Single Molecule Photon Cryocooler(SMPC) was built in generally meaning. Quantum transitions in single molecule

which was excited by photons with different energy and treated as a cryocooler

were simulated with computer. Frequencies and number of phonons

which participate in thermal excitation in ground state and in excited states and during fluorescence emitting

were studied. The conclusion that single molecule in ground state has more cooling power was obtained. So in optical absorption and emission process

the thermo dynamic effect in ground state is different from that in excited state for fluorescent cooling of single molecule. So

when we choose cooling material for anti Stokes fluorescent cooling usage

splits of the energy level in ground state of luminescence center is more important than in excited state.