The thermodynamic behavior of single molecule-photon cryocooler(SMPC)was described by the study of participating frequency of phonons in light transitions, heat-light converting efficiency and cooling efficiency. The times of heat distribution were taken as a time scale in the investigation of cooling efficiency. The cooling efficiency curve obtained from our theory has the same shape of experiment curves obtained by other researchers. The reason of a bending of cooling efficiency curve appearing in the cooling region was given. The greatest cooling efficiency of SMPC was investigated, and it is obtained that the best wavelength, which results in the greatest cooling efficiency,is located at the point of one fourth exciting band width from the red edge. As a main conclusion, crystal-line materials are the sole kind of promising materials for obtaining the greatest cooling efficiency.