The invention provides a fast hash vehicle retrieval method based on multi-task deep learning. The fast hash vehicle retrieval method includes a multi-task deep convolutional neural network used for deep learning and training recognition, a segmented compact hash code and instance feature fusion method for improving the retrieval accuracy and the practicality of the retrieval method, a local sensitive hash reordering algorithm for improving the retrieval performance and a cross-modal retrieval method for improving the robustness and accuracy of a retrieval engine. In the fast hash vehicle retrieval method, firstly, a method for segmented learning of hash codes through a multi-task deep convolutional network is proposed, image semantics and image representation are combined, the connectionbetween related tasks is used for improving the retrieval accuracy and refining image features, and at the same time, minimizing image coding is used for making learned vehicle features more robust; secondly, a feature pyramid network is used for extracting the instance features of vehicle images; then, a local sensitive hash reordering method is used for retrieving the extracted features; and finally, a cross-modal assisted vehicle retrieval method is used for the special case in which target images of inquired vehicles cannot be obtained.