Aiming at the problems of slow detection and low recognition accuracy of road traffic signs in Chinese intelligent driving assistance system, an improved road traffic sign detection algorithm based on YOLOv3 （You Only Look Once version 3） was proposed. Firstly, MobileNetv2 was introduced into YOLOv3 as the basic feature extraction network to construct an object detection network module MN-YOLOv3 （MobileNetv2-YOLOv3）. And two Down-up links were added to the backbone network of MN-YOLOv3 for feature fusion, thereby reducing the model parameters, and improving the running speed of the detection module as well as information fusion performance of the multi-scale feature maps. Then, according to the shape characteristics of traffic sign objects, K-Means++ algorithm was used to generate the initial cluster center of the anchor, and the DIOU （Distance Intersection Over Union） loss function was introduced to combine DIOU and Non-Maximum Suppression （NMS） for the bounding box regression. Finally, the Region Of Interest （ROI） and the context information were unified by ROI Align and merged to enhance the object feature expression. Experimental results show that the proposed algorithm has better performance, and the mean Average Precision （mAP） of the algorithm on the dataset CSUST （ChangSha University of Science and Technology） Chinese Traffic Sign Detection Benchmark （CCTSDB） can reach 96.20%. Compared with Faster R-CNN （Region Convolutional Neural Network）, YOLOv3 and Cascaded R-CNN detection algorithms, the proposed algorithm has better real-time performance, higher detection accuracy, and is more robustness to various environmental changes.