So SPMMF is easier to be implimented t echanically compared with the side polished singlemode fiber. To develop side polished multimode fiber (SPMMF) sensor,the optical power transmitting characteristics in SPMMF are analyzed.First we utilize BPM to simul ate and calculate the distribution of light intensity and mode field in SPMMF with different remaining radii,and the relation between the transmitted light power in fiber and the index of refraction of cover material i n polished area is derived as well.furthermore,we demonstrate our conclution wit h experiment.The results show that when the index of refraction of cover materia l in polished area is smaller than 1.44,the transmittance of light power in fiber is close to the transmittance in air; When the index of refraction of cover material in polished area increases to 1.458,the transmittance decreases to the minimum,and the minimum is not less than 0.001;When the index of refraction of cover material in polished area is lager than 1.458,the transmittance increases slowly and remains at a relatively stabl e value.The transmittance of the transmitted light power in SPMF will be affected by remaini ng radius.We conclute that the transmittance of the transmitted light power in SPMF is smaller as the remaining radius is smaller.