A new-type off-axis fiber optic rotary joint with large inner diamet er is designed to achieve the transmission of the optical signal between the rotary systems.The fiber collima tors and infrared right angle prisms are arranged in the flanges by a specific way,so that the optical sign al can be continuously transmitted in a larger off-axis offset.The main factors which affect the coupling efficiency o f the off-axis optical signal transmission are also analyzed.The coupling loss of the off-axis fiber optic r otary joint is further reduced by optimizing the thermally expanded core fiber collimator and the infrared right a ngle prism.The off-axis fiber optic rotary joint with the flange inner diameter of 60mm is fabricated,the numbers o f thermally expanded core fiber collimators on the inner and outer flanges are 16and 17,respectively,and the pa rallel optical transceivers are used to transmit and receive the serial optical signal.The experimental results of t he fiber optic rotary joint indicate that the maximum optical insertion loss of the off-axis fiber optic rotary joint is 21.73dB when the rotation rate of the flange is 60r/min and the signal transmission rate is 1.25Gbit/s,which can meet the requirement of stability for optical signal transmission between the ro tary systems.