Coverage guided Fuzzing is currently the most effective technology for automatic discovering vulnerabilities in a program. At present, most popular Fuzzing tools implement a full tracking strategy for newly generated test cases. But over time, most of them always focus on the highly frequent paths of the program and are unable to generate any new coverage. As a result, the strategy costs a lot of meaningless time and running overhead. In this paper, we propose a new tool called ADFuzz based on an anomaly detection model. Firstly, ADFuzz filters out rare paths to extremely reduce the number of test cases on frequent paths so as to speed up Fuzzing. Then, it constantly guides Fuzzing to mutate towards the targets of rare paths in order to generate new coverage. ADFuzz are tested on 12 real programs for 24 hours running with the same configuration as to AFL and Untracer. Compared with AFL, ADFuzz is 23.8% faster on average, averagely increases 11.78% and raises 25.8% at most on the percentage of coverage. Compared with Untracer, ADFuzzer makes much improvement on the number of crashes and the percentage of coverage while it has almost the same average speed.