In this paper, we give descriptions that the choices made in the Knowledge modelling or representation in Computer Evironments can modify the meaning of this knowledge through a process similar to that of the didactical transpostion. Thus, they are likely to have effects on learning. These problems and phenomena are consequences of general constraints of computer and an algorithms built-in computers. Students may not learn the knowledge intended by teacher. Teacher is always on the alert for the changable mathematical knowledge in computer-based environments. It is an important role of teachers in new teaching and learning environment.