As an important part of overhead transmission line, the safety of transmission tower will affect the operation of the whole power system. The construction of bird's nest is one of the important factors affecting the normal operation of transmission line, which needs to be monitored. Nevertheless, the existing monitoring methods not only are inefficient, but also require a lot of manpower and material resources. To cope with this phenomenon, this study puts forward a real-time detection method based on the algorithm of SSD. In addition, lead network VGGNet is replaced by ResNet-101 based on the network structure of SSD, so as to improve their ability of feature extraction. The Focal loss instead of Softmax loss improve SSD sample imbalances in the algorithm. And the data augmentation is used to increase diversity, in order to improve the robustness of the model. Experimental results show that the detection accuracy of the method proposed in this study is improved by 3.17% and 6.35% respectively in terms of accuracy and recall rate compared with the original SSD algorithm.