Although there are many methods to identify structural damage of the crane girder, almost all of them are used by means of comparing specific parameters of original and existing structures. And it leads to difficulties in practice. So, a method to identify damage of the crane girder is proposed based on strain modal without original model. First, the strain modal difference curve was obtained by using difference algorithm to deal with strain modal and cubic spline interpolation algorithm to fit the curve, and the damage location was realized by constructing and comparing damage sensitive index (IDSI). Then, the data of undamaged checkpoints adjacent to damaged checkpoints are stationary and modeled by Auto-Regressive Moving-Average Model, with this modeling the original data of the damaged checkpoints was predicted, and variation of the got strain modal difference curve was used to determine damage degree. Finally, the application of this method was implemented by some experiments and numerical calculations, and the results demonstrated that this method can effectively identify the damage of the crane girder.