Abstract: Taking the probes-rotating ultrasonic testing equipment as an example, according to the requirements of 100% transverse detection coverage, this paper simulates and analyses the relationship between the multi-probes layout, quantity, position and pitch of multi-probes etc. The paper provides a basis for the design and the use of the probes-rotating ultrasonic device. The analytical method can be used to make sure the scanning pitch on the scanning longitudinal defects, layered defects for the probes-rotating ultrasonic testing device. The conclusions obtained in this paper can also be used in other similar ultrasonic spiral scanning and testing equipment.