Abstract: Due to the fact that there is no A-scan display in a fully-focus phased array system, so this might cause some difficulties for the defect detection. By studying the sound field characteristics and signal characteristics of the fully-focus phased array, a new technical route of "field measurement" is proposed. The principle and the basic process of implementation were explained and the feasibility in the application of weld inspection was demonstrated. Some experiments were also given. It is pointed out that the presented field measurement technology route is beneficial to the unique characteristics of the fully-focus phased array technology and it can achieve good results.