The invention provides a method for rapidly detecting the comprehensive shading coefficient of an outer window on site. A comparison glass test piece is arranged on one side of an outer window test piece to be tested in parallel through a clamp, a first temperature sensor is adhered to the indoor side of the glass test piece by an adhesive, a second temperature sensor is mounted on the indoor sideof the electrochromic glass by an adhesive, the characteristic that the shading coefficient of the electrochromic glass is adjustable is utilized, and the shading coefficient of the electrochromic glass is quickly adjusted on site to be compared with the heat insulation performance of the glass test piece, so that it is quickly and accurately determined whether the outer window test piece meets the corresponding energy-saving design requirement or not. According to the invention, the comprehensive shading coefficients of different building outer windows are detected on site, the energy-savingperformance of the building outer windows is prevented from being satisfactory, and the energy-saving effect of the building outer windows is further ensured.