The invention discloses a biomarker capable of detecting diseases. The biomarker at least comprises one of the following microbes or the combination of the following microbes: Akkermansia muciniphila, Bacteroides fragilis, Clostridium bolteae, Clostridium hathewayi, Clostridium sp.HGF2, Clostridium symbiosum, Eubacterium limosum, Lactobacillus fermentum, Lactobacillus salivarius, Ruminococcus torques, Streptococcus anginosus, Streptococcus infantis, Bacteroides stercoris, Bacteroides uniformis, Bilophila wadsworthia and Clostridiales sp.SS3/4. The invention further discloses an application of the biomarker for determining inflammatory bowel diseases. The invention also discloses a method, a system and a kit for detecting the biomarker in a tested object. According to the invention, through the research on intestinal flora, and through the high-throughput genome sequencing, the biomarker with high relativity with the inflammatory bowel diseases is screened out, and then the biomarker is utilized for accurately and efficiently detecting and diagnosing the inflammatory bowel diseases, and further used for monitoring the treatment effect for the disease.