The invention discloses an FAM174B gene capable of serving as a molecular marker for early diagnosis of the coronary heart disease. It is found that a significant difference exists between expression of the FAM174B gene in blood of a normal person and expression of the FAM174B gene in blood of a patient suffering from the coronary heart disease, in other words, whether a subject suffers from the coronary heart disease or not can be judged by detecting expression of the FAM174B gene in blood. The invention further discloses a reagent kit for diagnosing the coronary heart disease according to the correlation between expression of the FAM174B gene and the coronary heart disease. The reagent kit is used for diagnosing the coronary heart disease by detecting expression of the FAM174B gene. The reagent kit can be used for early diagnosis of diseases and has broad clinical application prospects.