The load distribution analysis plays a significant role in the performance evaluation of cycloid speed reducer. However, current analytical models usually ignore elastic deformation, clearances, or assembly errors. These factors must be considered for realistic performance evaluation of cycloid speed reducer. This paper proposes an analytical model for cycloid speed reducer based on unloaded tooth contact and load distribution analyses. The proposed model can predict the loads on various components of the speed reducer in the presence of clearances and eccentricity errors. The results are compared with those predicted by the cycloid speed reducer model based on theoretical geometry. The effect of radial and pin-hole clearances as well as eccentricity errors, on some key design factors, such as contact stress, transmission error, gear ratio, and load on bearing, is investigated. This study can be used to assist the optimal design of cycloid speed reducers.