As the leading killer of human health in the current age, cancer is concerned widely in the medical profession. As the popularizations of atomic force microscopy (AFM) in micro-biology, measuring the mechanical properties of cells by AFM is gradually applied in the diagnosis and treatment of cancer. In this paper, the scanning parameters were optimized and the indentation experiments in different parts of oligodendrocytes were carried out to test the elastic modulus of oligodendrocytes. In order to evaluate the elastic modulus accurately, nine areas on each cell were selected, and for each area, a small matrix of indentation point was made. The results indicated that elastic modulus of the center part of cancer cell is softer than that in the edge, and the one of the normal cell are 3 order of magnitude harder than the cancer cell.