In the later stages of oilfield production, the high-temperature, high-salinity environment deep within the formation intensifies, making it difficult for existing polymer oil displacement agents to meet the requirements for increasing oil production and revenue. To develop polymer oil recovery agents capable of withstanding these harsh reservoir conditions, a strategy was adopted to construct a semi-interpenetrating network structure. Polyvinylpyrrolidone (PVP) was used as the linear polymer, and polyvinyl alcohol (PVA) crosslinked with epichlorohydrin (ECH) served as the crosslinking network, resulting in a temperature- and salt-resistant semi-interpenetrating PVP-in situ-PVA hydrogel. The hydrogel’s tolerance to temperature and brine of varying salinities was investigated, and its network structure and properties were analyzed. The results indicate that when the mass fractions of ECH and PVP are optimized to 1.7 wt% and 0.67 wt%, respectively, the PVP-in situ-PVA hydrogel exhibits the highest compressive strength of 0.30 MPa. Furthermore, the PVP content significantly influences the mechanical properties and thermal and salt resistance of the PVP-in situ-PVA hydrogel. The viscoelastic particle oil displacement agent PVP0.67/PVA PPG prepared in this study retains 46.2% of its modulus after aging at 90 °C for 20 d, outperforming the PVP0/PVA PPG without PVP.