Despite the high demand for strong, lightweight, and tough Aluminum Matrix Composites (AMCs) across various applications, achieving desired property compatibility remains challenging due to limited control over the reinforcement processes. A novel AMC has been developed and synergistically reinforced with transgranular microscale Al3Ti, sub-microscale TiN, and intergranular nanoscale AlN, through Ti2AlN and Al in situ reaction. The in-situ multiphase-and-scale structure, resulting from the intricate reaction mechanisms and N interstitial solution, was analyzed using experimental investigations, thermodynamics and kinetics calculations, while the robust interfacial properties were studied by first-principles calculations. Both endowed the composite with exceptional strength (776 MPa and 635 MPa for compressive and flexural strength). Strengthen mechanisms were composed of fine-grain, solid-solution, and dislocation strengthening. This work succeeds in refining Al3Ti particles and creatively breaks through the bottleneck of synthesizing multi-dimensional and tunable in-situ reinforcements, expected to open new avenues for developing and applying a new generation of advanced AMCs.