Abstract: Because of the complexity in studies on software code and software network, the software-kernel of software network is defined and extracted to reduce the difficulty of grasping and measuring any software. Then a software-kernel layer stripping algorithm is developed to study the software-kernel with a certain amount of samples. The analysis results showed that the ordinal number of software-kernel layer of any software is directly proportional to the growth of that software, i.e. its upgrading evolution. The ratio of ordinal number of a kernel layer to the number of nodes of a software-kernel thus approximates to the S-model during the growth of software. Such a result is available to study the hierarchy of measuring softwares. Moreover, the extraction of software-kernel can be used to simplify the grasping of softwares and focus on the design, implementation and testing of key classes in softwares.