Aiming at the structure feature of plagiarized source code, this paper proposes a kind of visual positioning recognition method based on the function domain mode of source code. According to the basic structure feature of source code, function domain is taken as the key point of visual recognition. In this method, the index of each function domain is recorded at first. Then it applies string matching algorithm at the layer of identifiers to corresponding functions in order to locate the similar areas and build the index map in source codes. At last the plagiarism areas are outstanding displayed by heterochromatic mark so as to achieve a visual effect of positioning domain. At the same time of visual recognition, the system also provides comparison and estimation of different ways. Practice proved that for the detection of common source code plagiarism in teaching, the method can do the visual recognition accurately, and the accuracy can reach 90%.