The baculovirus expression system utilizing Bombyx mori nucleopolyhedrovirus (BmNPV) in silkworm larvae is a powerful tool for recombinant protein production, but it is often limited by viral-induced host liquefaction and proteolytic degradation. To address this, a double-deletion BmNPV bacmid lacking both cysteine protease and chitinase genes (BmNPV-CP−-Chi−) was constructed. This modification successfully prevented larval liquefaction, abolished the degradation of the target protein, and significantly improved the stability and yield of secreted protein. Furthermore, transcriptional efficiency was enhanced by engineering the very late polyhedrin (polh) promoter with multiple burst sequences (BSs). While two BSs were optimal for expression in cultured insect cells, a modified promoter harboring nine BSs maximized β1,3-N-acetylglucosaminyltransferase 2 (β3GnT2) expression in silkworm larvae, achieving a 6.8-fold increase in enzymatic activity. Additionally, the coexpression of very late transcription factor 1 (VLF-1) synergistically augmented target protein production by further stimulating the engineered polh promoter. In conclusion, the integration of protease/chitinase gene deletions with targeted polh promoter modifications establishes a highly robust, high-yielding platform for large-scale eukaryotic recombinant protein production in silkworm biofactories.