Current end-to-end detectors typically exploit transformers to detect objects and show promising performance. Among them, Deformable DETR is a representative paradigm that effectively exploits multi-scale features. However, small local receptive fields and limited query-encoder interactions weaken multi-scale learning. In this paper, we analyze local feature enhancement and multi-level encoder exploitation for improved multi-scale learning and construct a novel detection transformer detector named Augmented DETR (AugDETR) to realize them. Specifically, AugDETR consists of two components: Hybrid Attention Encoder and Encoder-Mixing Cross-Attention. Hybrid Attention Encoder enlarges the receptive field of the deformable encoder and introduces global context features to enhance feature representation. Encoder-Mixing Cross-Attention adaptively leverages multi-level encoders based on query features for more discriminative object features and faster convergence. By combining AugDETR with DETR-based detectors such as DINO, AlignDETR, DDQ, our models achieve performance improvements of 1.2, 1.1, and 1.0 AP in the COCO under the ResNet-50-4scale and 12 epochs setting, respectively.