Disclosed in the present invention is an aqueous secondary dispersion containing a copolymer P. The copolymer P is synthesized from the following components: 1) a hydroxyl-containing hydrophobic polymer comprising the following components as structural unit monomers: a hydroxyl-containing monomer A1, and an acrylate monomer and/or ethylene monomer B1; and 2) a hydroxyl-containing hydrophilic polymer comprising the following components as structural unit monomers: a hydroxyl-containing monomer A2, an acrylate monomer and/or ethylene monomer B2 of which a homopolymer having Tg greater than 80°C, an acrylate monomer C of which a homopolymer having Tg less than 80°C, and a carboxyl-containing monomer D. The thickness of a non-bubble film of the dispersion is relatively high while other properties such as hardness and resistance are not significantly lost; moreover, the dispersion is good in weather resistance, and can tolerate a low-humidity, especially high-temperature and low-humidity construction environment. Also disclosed in the present invention are a preparation method for the dispersion, and an application of the dispersion.