According to the experience of making computer assisted inst ruct ion ( CAI ) co urseware, it w as pointed out that CA I system is both computer system and teaching system in this paper. T o a certain ex tent , coursew are w ith teaching funct ion should ref lect teaching theory, teaching tact ics, study ing theory and theory of CAI design. In view of human thinking peculiarity as w ell as ov erally t raining and developing human abil ity , the examples w ere g iven to ex plain the pro jection’ s specific proper ty of ‘parallel of project ile face’ and ‘vert ical of pro jectile face’in this paper. It w as show n by co ncretely apply ing that method of logical thinking of both induct ion and deduct ion.