We have demonstrated a kind of single-end reflective optical fiber Mach-Zehnder (M-Z) interferometer based on large lateral-offset splicing joints. Several hundred microns of standard single-mode fiber (SMF) was spliced between two other SMFs with the same lateral offset. One fiber has its end-face coated by gold film, acting as a reflector. The beams propagating in the environmental medium and the fiber cladding material interfere and produce a phase difference. The reflected interference spectra were measured at the same side of the broadband source by an optical spectrum analyzer. The pattern of interference spectrum shifts with the change of the external refractive index (RI). The sensor with a cavity length of 554 μm and a lateral offset of 62.5 μm is demonstrated. The achieved RI sensitivity in water and the temperature coefficient in air are -13257 nm/RIU and 37.33 pm/℃, respectively. Compared with the reported counterparts, the sensor has the advantages of high refractive index sensitivity, compact structure, single-ended measurement and good stability, and has good application prospects in the fields of biochemical sensing and environmental pollution monitoring.