Focusing on the increasing amount of test data in the development of Very Large Scale Integration (VLSI), a test data compression method based on tri-state signal was proposed. Firstly, the test set was optimized and pre-processed by performing partial input reduction and test vector reordering operations, improving the compatibility among test patterns while increasing the proportion of don't-care bit X in the test set. Then, the coding compression of tri-state signal was performed to the pre-processed test set, so that the test set was divided into multiple scan slices by using the characteristics of tri-state signal, and the tri-state signal was used to perform compatible coding compression on the scann slices. With various test rules considered, the test set compression ratio was improved. The experimental results show that, compared with the similar compression methods, the proposed method achieves a higher compression ratio, and the average test compression ratio reaches 76.17% without significant increase of test power and area overhead.