An effective linking and coupling method for single core single mode fiber (SMF) and capillary optical fiber is proposed. Two types of capillary optical fiber which have different structures are investigated. By splicing and tapering at the fusion point of single mode fiber and capillary optical fiber, an effective bi-tapered fiber coupling technique is implemented. The coupling mechanism and the transmission properties are studied and compared. The theoretical prediction is confirmed by the experimental results. The coupling approach is simple and efficiency.