Abstract: In order to improve the accuracy of the of small traffic signs detection in complex natural traffic scenes,an improved SSD algorithm is proposed.Parallel multi-scale feature fusion was added to multiple detection layers of SSD.The combination of shallow and deep features compensated the disadvantages of the SSD model in its detections of the small targets.The attention mechanism was added in multiple detection heads of SSD model to enhance the feature extraction effect of small traffic signs.The focal loss function was applied to reduce the effect of the background to the overall loss and avoid overfitting to the background.The experimental results show that the mPA of detecting small traffic signs with the improved SSD model in the complex natural scenes is improved by 4.9 percentage points compared with the original model.