To enhance the application of water-stopping and leakage-plugging materials in water-rich strata and wide crack sections with load demand, we developed a hybrid network composite material by combining poly(magnesium acrylate) acrylate and cement. This material exhibits superior performance in both organic and inorganic phases, offering broader potential applications than pure poly(magnesium acrylate) acrylate. However, it is susceptible to system instability and cracking attributed to water loss and shrinkage properties. In response, we conducted research to investigate the impact of maintenance conditions, polyash ratio, and various additive dosages on the water loss properties of poly(magnesium acrylate)/cement composites. The analysis of the water loss process involved curve fitting, and we established a multiple regression prediction model. Our findings reveal three stages of water loss for the material: isokinetic water loss, decelerated water loss, and smooth water loss. The implementation of water conservation measures significantly enhances material stability. Particularly noteworthy is the substantial influence of the poly-ash ratio on water loss performance. The optimal formula, derived from our study, is as follows: poly-ash ratio of 1, initiator dosage of 1.5%, and crosslinking agent dosage of 1.0%.