In 2018, YL Co., Ltd. as the only private listed company in the coal sector, defaulted on bonds, which was started by the debt default of "17 YL CP004". Based on the modified ZChina-score model, this paper calculates the z-value of YL Co., Ltd.in the five years before its default, and analyzes the credit rating of YL Co., Itd. with the rating agencies in the same period to verify the applicability of the modified ZChina-score.