Boundary-Scan Technique(BST) is a new and effective way of test and design-for-testability for VLSI circuits. In order to use BST more efficiently, it is necessary to study the basic theory of boundary-scan test thoroughly and precisely. In this paper, A mathematical model of boundary-scan test process is set up based on Boolean Matrix theory. Then, by applying the model established, two boundary-scan test generation principles are presented. The first one gives the sufficient condition for fault detection in boundary-scan test. The second gives the sufficient condition for fault isolation and diagnosis in boundary scan test. The mathematical model and its deduction constitute the theoretical basis of boundary scan test, which can be used in developing test generation algorithms with better property.