The pathogenic detection and epidemiological investigation of one patient with diarrhea that had not been cured for a long time were carried out.The pathogen was identified by direct smear of fecal samples and hematoxylin stain-ing,and epidemiological investigation was carried out to analyze its infectious disease characteristics.Giardia lamblia infec-tion was found,and the prognosis was better with corresponding treatment.It is recommended that college students should live a regular life,improve poor eating habits,seek medical attention in time if they have diarrhea,and review their stool rou-tine examination if necessary.