1. Wind compressive strength and water tightness: Plastic steel doors and windows are about two grades lower than aluminium alloy doors and windows because of their low material strength and steel properties, although they have been strengthened by adding lining. This is the case with the standard sample windows sent by the enterprises for inspection, and the same is true with the sampling at the construction site. The average value of "three properties" measured by Shanghai Curtain Wall Inspection Center for aluminium alloy doors and windows and plastic steel doors and windows installed in the construction site by witness sampling method shows that "except air tightness, the water tightness and wind pressure resistance of plastic steel doors and windows are worse than those of aluminium alloy doors and windows, which is unexpected, but further graded. The analysis reflects the important quality problems of plastic steel doors and windows. Moreover, because the lining steel of plastic-steel doors and windows is not connected into a complete frame system at the corner of the inner cavity of the profiles, the plastic welding angular strength of window frames, fan corners and T-byte points is relatively low.