In order to delay the gelation time of polymer gel，a micro-nano sustained-release（MNSR）gel was prepared using partially hydrolyzed polyacrylamide，crosslinking agent J₁（chromic acetate）and J₂（phenolic resin），D-isoascorbic acid and hydrophobic fumed silica as raw materials. The crosslinking agent solution was encapsulated by the self-assembly of hydrophobic particles in aqueous solution，and then added into a polymer solution，as a result，the purpose of delaying the gelation time was achieved by slowly releasing the crosslinking agent. The influence of pH value on the encapsulation ability of hydrophobic particles and the concentration of hydrophobic particles on the thermal stability of capsules，gelation time and gel strength were studied. Experimental results showed that the pH value of the solution suitable for the sustained-release capsule was 2—10. When the particle concentration in the capsule was 10%，the water separation rate of the capsule was 3.33% at 30 ℃ and 26.67% at 120 ℃ after 240 h. When the capsules with a particle concentration of 10% were used，the gelation time of the gel was extended from 48 h to 486 h at the temperature of 30 ℃，and was extended from 1 h to 144 h at the temperature of 120 ℃. The gel storage modulus G' of the gel before adding the capsule was 43 Pa and yield stress was 102 Pa，while the G' of MNSR gel was 313 Pa and the yield stress was 202 Pa. The sustained-release capsules prepared by hydrophobic particles had better thermal stability，which not only delayed gelation time，but also increased the gel strength.