To explore the molecular genetic mechanisms of cytoplasmic male sterility in sugar beet, the differential proteins between the CMS line and its maintainer line were studied. Immobilized pH gradient two-dimensional gel electrophoresis (2-DE) technique and MALDI-TOF-MS were used to identify differentially expressed proteins in the three pollen development stages(stamen primordium differentiation stage, metaphase and uninucleate stage) between the Owen sugar beet male-sterile line(DY5-CMS)and its maintainer line(DY5-O). Six distinct proteins were identified in the stamen primordium differentiation stage and four distinct proteins were identified in the metaphase. In addition, all those proteins were related to the energy and respiratory metabolism. It was inferred that cytoplasmic male sterility of sugar beet might take place at the prophase of pollen development(contain stamen primordium differentiation stage and metaphase). The over-expression of energy and respiratory metabolism related proteins leads to metabolism disorder. Six distinct proteins are identified in the uninucleate stage of pollen development, and most of the proteins are related to photosynthesis of plants. It is speculated that the male sterility trait has formed at the late stages of pollen development and male sterility leads to the decreasing of photosynthetic.