The primary findings are as follows: the serum S1P level was significantly increased in both IPF and CTD-UIP patients, while IPF and CTD-UIP showed comparable S1P levels; In CTD-UIP patients, but not IPF patients, serum S1P level showed significantly negative correlation with pulmonary function change and positive correlation the length of hospital stay, which represents the severity of CTD-UIP; the association value of serum S1P with pulmonary function was further confirmed by linear regression. This evidence concerns the gene MBTPS1 and idiopathic pulmonary fibrosis.