Spatiotemporal forecasting tasks, such as traffic flow, combustion dynamics, and weather forecasting, often require complex models that suffer from low training efficiency and high memory consumption. This paper proposes a lightweight framework, Spectral Decoupled Knowledge Distillation, which transfers the multi-scale spatiotemporal representations from a complex teacher model to a more efficient lightweight student network. The teacher model follows an encoder-latent evolution-decoder architecture, where its latent evolution module decouples high-frequency details (e.g., instant traffic fluctuations) and low-frequency trends (e.g. long-term weather evolution) using convolution (local high-frequency extractor) and Transformer (global low-frequency modeler). However, the multi-layer convolution and deconvolution structures result in slow training and high memory usage. To address these issues, we propose a frequency-aligned knowledge distillation strategy, which extracts multi-scale spectral features from the teacher’s latent space, including high and low frequency components, to guide the lightweight student model (e.g., ResNet, U-Net) in capturing both local fine-grained variations and global evolution patterns. Experiments show that the student model achieves over 95% of the teacher’s forecasting accuracy while using only 20%-30% of its memory, with training speed improved by more than 50%. Our theoretical analysis reveals that the frequency-domain decoupling enables the student model to capture long-range dependencies without the need for complex structures. The frequency-aligned distillation mechanism further mitigates the inherent bias of lightweight models in cross-scale spatiotemporal dynamics modeling. This framework offers an effective and general solution for high-accuracy spatiotemporal forecasting in resource-constrained scenarios.