In order to solve the problem that is difficult to layout strain sensor on the compact mechanical structure to measure stress. From the dynamics point of view, the equivalent forces of actual forces are built applying the pseudo-forces technique, and pseudo measurement points computationally are put on the mechanical structure to overcome the problem is short of measurement points. A new method to calculate structural strain using acceleration response signal of mechanical structural under operation condition is put forward in the paper and has been verified by engineering example. The research results are shown that the new method can be used to analyze the strain data where the mechanical structures are compact and not suitable for experiment of strain. The method lays the groundwork for fatigue life analysis.