The application discloses a method for determining a standard for judging negative and positive property of an unknown sample, a method for improving detection accuracy of cell surface antigen expression and a device for detecting negative and positive property of the sample. A body liquid sample to be detected is mixed with a fluorescent detection agent to obtain dyed sample fluid to be detected. The sample fluid to be detected is detected by a flow cytometry to obtain fluorescence intensity of the sample fluid to be detected. Difference of fluorescence intensity between the sample fluid to be detected and an isotype control is calculated. The difference and a preset fluorescence critical value are compared and cell surface antigen expression is judged according to the comparative result. According to the application, a suitable value is determined as the fluorescence critical value, interference of non-specificity combination to the detection result is reduced and accuracy of the detection result of the HLA-B27 antigen expression is improved.