Stress concentration is the key factor that induces the damage of oilgas pipeline. It is a serious threat to the safe of pipeline. Effective test can both find the mechanical damage induced by stress concentration and achieve prejudgment of early damage of pipeline. Magnetic memory technology has been widely recognized by the customers as a method of stress testing. In this paper, magnetic memory signal character of ferromagnetic material in different stress application is analyzed in the macroscopic and microcosmic range from the point of energy balance. The theory relation model between stress and susceptibility or atomic magnetic moment is build. Force magnetic coupling process of magnetic memory in FeC metal system is simulated by CASTEP software, which is based on first principle. The results show that ferromagnetic system energy balances and achieves to stable state when the stress is applied. It also weakens the material magnetism and changes the distribution character of electron band structure and density of state. Atomic magnetic moment and susceptibility decrease linearly along with the increase of stress. Finally, magnetic memory testing experiments on pipeline contained crack demonstrate the correctness of theory analysis and effectiveness of engineering application.