Abstract: The Christmas tree equipment is one of the key equipments in the process of oil and natural gas production, but a lot of trees are rarely maintained and inspected once put into use, this will have a very big security risk. So, it is necessary to detect without stop production,but the current standard and conventional detection methods can not meet the need. We find out the technology about inspecting Christmas tree with ultrasonic-phased-array and find out the specific parameter setting, and its accuracy is verified by experiment through studing of the artificial defects, and simulating various types of the defects possibly and in different parts of the defects, and through continuous improvement and debug. The study in this work shows the advantages of the ultrasonic-phased-arrays inspection technique,providing a foundation for the engineering application of using ultrasonic-phased-arrays inspection technique to detect the Christmas tree equipment.