Stacking　order　critically　influences　the　optoelectronic　properties　of　2D　van　der　Waals　materials.　Here,　first-principles　calculations　were　performed　to　study　the　geometries,　band　structures,　and　second-harmonic　generation　(SHG)　of　hexagonal　boron　nitride　(h-BN)　bilayers　constructed　by　the　relative　shifts　and　rotations　between　h-BN　layers.　Our　results　indicate　that　the　stability,　interlayer　coupling,　and　band　structures　of　h-BN　bilayers　are　sensitive　to　the　stacking　orders.　For　interlayer　sliding,　the　direction　and　size　of　lateral　displacement　obviously　affect　the　band　gap　and　components　at　the　band　edge.　By　contrast,　the　band　structure　of　twisted　h-BN　bilayers　is　highly　angle-dependent,　and　when　the　sum　of　twist　angles　in　two　moire　superlattices　is　60　degrees,　they　have　similar　band　structures　due　to　identical　band　folding.　As　for　the　second-order　susceptibility,　interlayer　sliding　tends　to　enhance　the　SHG　intensity　compared　to　that　of　the　original　AA　stacking.　When　the　incident　angle　of　the　pump　light　deviates　from　the　normal　direction　of　the　h-BN　bilayer,　the　change　in　lattice　symmetry　induced　by　interlayer　sliding　results　in　distinct　variations　in　SHG　patterns,　thereby　facilitating　identification　of　the　corresponding　structures　through　polarization-resolved　SHG　spectroscopy.　For　twisted　configurations,　as　the　rotation　angle　increases　from　0　to　60　degrees,　the　evolution　of　SHG　intensity　departs　significantly　from　the　coherent　superposition　model　due　to　the　strong　exciton　effects　in　h-BN　bilayers.　Although　the　interlayer　rotation　preserves　the　SHG　polarization　image,　the　experimental　measurement　of　relative　SHG　intensity　enables　the　determination　of　the　rotation　angle,　which　allows　for　distinguishing　structures　of　twisted　h-BN　bilayers.