Through-glass-via (TGV) technology has great potential for various applications in advanced electronic packaging and integrated passive devices due to its excellent electrical/optical properties, favorable mechanical stability and low cost. Nonetheless, the manufacturing of TGV packages is often impeded by molding warpage, which is caused by the large coefficient of thermal expansion (CTE) mismatches among packaging materials such as semiconductors, metals, and molding compounds. This warpage not only creates troubles in subsequent manufacturing processes but also degrades the performance and reliability of the final devices or packages. This study investigated the characteristics of warpage during molding process by finite element simulations and experiments for the state-of-the-art 2.5D glass interposer packages. A cell model was established to homogenize the micro-bumps, underfill, and the re-distribution layers (RDLs) for simplifying the package structure. A wafer-level glass interposer packaging process based on TGV and molding was proposed. The warpage values were measured by a laser-assisted method, and the simulated values agreed well with the experimental measurements. Furthermore, the effect of different molding and glass materials on warpage was explored. This study provided a viable approach to predict the wafer-level molding warpage and optimize process parameters to reduce warpage and improve packaging reliability.