The development of microspherical cavity theory is introduced,and the microspherical cavity is analyzed with light quantum mechanics.The 1533 nm fluorescence spectrum of the Er3+ doped phosphate glass microsphere(about 15 μm in diameter) was measured under laser excitation of 488 nm.The phenomenon of the morphology-dependent resonances of the fluorescence spectrum in the glass microsphere and its formation mechanism were observed and analyzed.The fluorescence spectra of the Er3+doped phosphate glass microsphere were compared with those of corresponding bulk glass.The single-mode oscillation amplitude generated by the Er3+ doped phosphate glass microsphere was obtained in the experiment.