Detecting is a key technology which has widely been used in almost all fields. However, there are two problems in traditional detecting methods. First, some physical value can not be detected; Second, it is difficult to improve the accuracy according to the way currently in effect. In this paper, based on the transformation concept of the contradiction, a new detecting technology—extension detecting technology (EDT) , which is totally different from the existing ones is developed. EDT takes advantage of the concept of matter element and the related methods of extrinsic. It use the transformation of matter element to study detecting technology. In order to solve detecting problems of undetectable physical value the related concepts, basic principle and frame of extension detecting technology are introduced. An implementing way for its application to engineering is proposed, and an example is given as well.