The invention relates to a piece of colloidal gold test paper for quickly detecting di-n-octyl ortho-phthalate and a preparation method thereof. The colloidal gold test paper for quickly detecting di-n-octyl ortho-phthalate comprises a reaction membrane, a sample pad, a ligature releasing pad, a water-absorbing pad and a backing liner, wherein a test area for a di-n-octyl ortho-phthalate carrier protein conjugate and a goat-anti-rat IgG quality control area are wrapped on the reaction membrane, and a di-n-octyl ortho-phthalate monoclonal antibody, namely, colloidal gold marker, is wrapped on the ligature releasing pad. The colloidal gold test paper provided by the invention has the advantages of simpleness in operation, low cost, high sensitivity, high detecting speed, suitability for large-scale application, capability of testing on site, suitability for screening of a large quantity of samples, no requirement for special instrument and professional staff, and easiness in application and implementation.