Abstract: Orthogonal experiments were conducted to fabricate AerMet100 high-strength steel via laser metal deposition (LMD). The microstructure and mechanical properties of the deposited alloy were systematically investigated using optical microscopy (OM), scanning electron microscopy (SEM), electron probe microanalysis (EPMA), microhardness testing, room-temperature tensile testing, and impact testing. Results indicate that the optimal linear energy density range for LMD-processed AerMet100 steel is 170 ~ 250 J/mm. The deposited microstructure consists of columnar cellular crystals containing lath martensite along the solidification direction and residual austenite at cellular dendrite boundaries. The lath martensite forms through rapid cooling-induced austenite transformation during laser processing, while the residual austenite primarily results from the segregation of austenite-stabilizing elements (Cr, Mo, Ni) during solidification. The hardness of the as-deposited matches that of the matrix, but heat accumulation during deposition induces high-temperature tempering of the matrix's tempered martensite, creating significant heat-affected zone (HAZ) softening along the deposition direction. Process optimization enabled the laser-deposited AerMet100 high-strength steel to achieve superior comprehensive mechanical properties at laser power P = 1700 W and scanning speed V_s = 10 mm/s, demonstrating ultimate tensile strength of 1 865.3 MPa, yield strength of 1 585.5 MPa, and elongation of 12.4%. Fracture morphology analysis reveals that decreasing linear energy density eliminates shear lips on tensile fracture surfaces, reduces dimple depth, increases cleavage facets on impact fracture surfaces, and shifts fracture mode from ductile to brittle.