Title: Lossless Filter Pruning via Adaptive Clustering for Convolutional Neural Networks. Abstract: The filter pruning method introduces structural sparsity by removing selected filters and is thus particularly effective for reducing complexity. However, previous works face two common limitations. 1) The pruned filters are prevented from contributing to the final outputs, resulting in performance degradation, especially when it comes to a large pruning rate. 2) To recover accuracy, the time-consuming fine-tuning step is required. The cost in time and the need for training data make it difficult to deploy in real-world scenarios. To address the aforementioned limitations, we propose a novel filter pruning method called Cluster Pruning (CP). Our CP reconstructs the redundant filters from the perspective of similarity and removes them equivalently using the proposed channel addition operation in a lossless manner. Pruning in such a way allows CP to preserve as many learned features as possible while getting rid of the need for fine-tuning. Specifically, each filter is first distinguished by clustering and then reconstructed as the centroid to which it belongs. Filters are then updated to eliminate the effect caused by mistakenly selected. After convergence, CP can equivalently remove identical filters through the proposed channel addition operation. The strategies for adjusting the pruning rate and the adaptive coefficient for clustering make our CP even smoother and more efficient. Extensive experiments on CIFAR-10 and ImageNet datasets show that our method achieves the best trade-off between performance and complexity compared with other state-of-the-art algorithms.