Since the discovery of graphene monolayers, a variety of 2D crystals have been explored both theoretically and experimentally. Most recently, domain-hybridized graphene and boron nitride (C-BN) monolayers have successfully been fabricated. Our research group has proposed a 2D superlattice monolayer consisting of well-aligned alternating graphene and boron nitride stripes and shown that this hetero-phase 2D crystalline monolayer is structurally very stable and electronically semiconducting. In this research, we further investigate the feasibility of tailoring the electronic property of C-BN monolayer superlattice by applying mechanical strain. Using the first-principles calculation based on density functional theory, we compute detailed electronic band structures of C-BN superlattices subject to mechanical strain, with respect to stripe width. The dramatic bandgap changes of armchair superlattices are presented and the mechanically tuned spin-polarized metallic properties of zigzag superlattices are demonstrated.