Abstract: To realize the in-depth conformance control for CO₂-flooding process, a kind of preformed particle gel with pH-responsiveness was designed based on labile cross-linking strategy. The gels were prepared via solution radical polymerization of acrylamide as monomer, with the incorporation of an acid-labile acetal as cross-linker, in addition to a stable one. The influences of acetal content, temperature and media pH on the swelling behavior were investigated. The obtained particle gel was exposed to brine and acidic buffer(pH value≤3.0), then it showed the swelling pattern of two-stage, while the conventional preformed particle gels prepared under the same conditions showed a single-stage swelling pattern. With the same content of stable cross-linker, the equilibrium swelling degrees in the two media decreased with the increasing of acetal content. In the neutral medium, the equilibrium swelling degree was almost not influenced by the temperature, while the swelling rate and equilibrium swelling degree increased with the increasing of temperature in acidic media. Accordingly, this kind of pH-responsive preformed particle gel with two-stage swelling behavior would have potentials as promising materials for in-depth conformance control in CO₂-flooding processes.