Concrete dam deformation prediction is important for assessing the safety of dams. A TPE-STL-LSTM deformation prediction model for concrete dams is established by introducing the TPE algorithm based on the decomposition–prediction model. Taking the Wanjiazhai gravity dam project as an example, a prediction model for the top deformation of 14 dam sections was established and the parameters were determined. The model was used for deformation prediction and compared with the measured deformation and similar methods to predict deformation for verification. The results show that the model has good prediction effect and matches well with the measured data; the accuracy is better than the Autoregressive Integrated Moving Average model and the Support Vector Machine model; and the model achieves the automatic determination of all parameters. The model can be used for dam engineering safety assessment, effectively improving the analysis accuracy and analysis efficiency.