Title: FTSO: Effective NAS via First Topology Second Operator. Abstract: Existing one-shot neural architecture search (NAS) methods generally contain a giant supernet, which leads to heavy computational cost. Our method, named FTSO, separates the whole architecture search into two sub-steps. In the first step, we only search for the topology, and in the second step, we only search for the operators. FTSO not only reduces NAS’s search time from days to 0.68 seconds, but also significantly improves the accuracy. Specifically, our experiments on ImageNet show that within merely 18 seconds, FTSO can achieve 76.4% testing accuracy, 1.5% higher than the baseline, PC-DARTS. In addition, FTSO can reach 97.77% testing accuracy, 0.27% higher than the baseline, with 99.8% of search time saved on CIFAR10.