Catalytic activity and stability, reflected in high conversion, heat sink, and time on stream, are the major concerns of endothermic hydrocarbon fuel cracking. In this work, we synthesized a stable MgAl2O4 spinel support by the co-precipitation method and a Pt/MgAl2O4 catalyst by the liquid-phase reduction-impregnation method (PMA-V) and incipient-wetness impregnation method (PMA). PMA-V showed a better catalytic activity and stability than PMA. Moreover, the heat sink and stability are significantly superior to the Pt-based catalysts in our previous published works. Through a series of catalyst characterization, we found that the high catalytic activity and stability over PMA-V are owing to the "accessible" Pt active sites with better dispersion and a smaller Pt size, which can efficiently alleviate Pt sintering, stronger metal-support interaction, suitable acidity-alkalinity, and a stable MgAl2O4 spinel structure. The valuable information provided in this work provides an effective approach to improve both catalytic activity and stability for hydrocarbon cracking.