As the maintenance of heat exchangers of nuclear power plants is extremely difficult to operate manually,this paper presents a scheme of using a robot to automatically inspect the exterior of heat transfer tubes. In the investigation,the robot is developed by a modular design approach and it mainly consists of a longitudinal mobile module,a rotary module,a locating module,an extending and retracting module,a micro vehicle module,a base,and three electrical motors. The micro vehicle carries a micro camera and can move in the transverse gap of tube bundles to perform video inspection on the target areas. Moreover,the form of 3-CSR parallel mechanism is proposed,and a micro 3-CSR parallel mechanism actuated by shape memory alloy ( SMA) coil springs is designed to adjust the micro camera pose. In addition,the control system is put forward,the acceleration and the deceleration curves of the longitudinal mobile module are designed based on fuzzy control theory,and a grey evaluation method is used to evaluate the inspection results. Experimental results from the prototyping system of the robot indicate that the robot can improve the quality and efficiency of inspection,thus meeting the design requirements.