The invention discloses an 
image retrieval method based on multi-task hash learning. Firstly, the deep 
convolutional neural network model is determined. Secondly, the 
loss function is designed by using multi-
task learning mechanism. Then, the training method of 
convolutional neural network model is determined, in combination with the 
loss function, and back propagation method is used to optimize the model. Finally, the image is input to the convolutionalal neural 
network model, and the output of the model is transformed into hash code for 
image retrieval. The 
convolutional neural network modelis composed of a convolutional sub-network and a full connection layer. The convolutional 
subnetwork consists of a first convolutional layer, a maximum 
pooling layer, a second convolutional layer, anaverage 
pooling layer, a third volume base layer and a spatial 
pyramid pooling layer. The full connection layer is composed of a 
hidden layer, a hash layer and a classification layer. The training method of the model includes two 
training methods: a combined training method and a separated training method. The method of the invention can effectively retrieve single tag and multi-tag images, and the retrieval performance is better than other deep hashing methods.