Based on the traditional colloidal strip, the pre-incubation reaction model was adopted, which was performed in the homogeneous aqueous solution between the colloid gold labeled antibody and analyte. This pre-incubation reaction was used to improve the efficiency of the immunoreaction. The pre-incubation solution was added to the colloidal gold strip for detection. Taking advantage of the pre-incubation model, the pre-incubated products were added to the colloidal gold strip for detection and the sensitivity for tetracycline was improved by 5 folds, as low as 1 μg/L. Changing the reaction model of the traditional colloidal gold strip from the direction adding sample to pre-incubation and adding sample could obviously improve the sensitivity of the traditional colloidal gold strip method.