Circumferential crack detection of small diameter tubes is a difficult problem to solve in eddy current testing. The three-dimensional simulation model is established through electromagnetic field simulation software to analyze the eddy current field distribution of the traditional bobbin probe and transverse cylindrical probe in small diameter tubes. The results show that the circumferential crack has a more marked disturbance to the eddy current field generated by the latter. Based on the simulation research, a new type of probe based on transverse excitation is designed to detect the artificial circumferential crack of the specimen with the designed probe, which can effectively detect the circumferential crack and has a potentially high sensitivity to the narrower natural circumferential crack.