ABSTRACTCarbon‐interstitial compounds of precious metal alloys (Ci‐PMA) have attracted increased attention as effective catalytic materials, but their precise and controllable synthesis remains significant challenges. Herein, we have established a universal approach for the straightforward synthesis of supported Ci‐platinum group metal‐indium alloys (M3InCx, M = Pt, Pd, Ni, x = 0.5 or 1). The control experiment results indicate that the C atoms in Pt3InC0.5 come from the solvent. Furthermore, 0.2 wt.% Pt3InC0.5/SiO2 exhibits excellent catalytic performance for aqueous phase reforming (APR) of methanol (CH3OH) to produce hydrogen, with productivity and turnover frequency of 310.0 −1mol·kgcat·h−1 and 30 126 h−1 at 200°C, which are 1.7 times greater than those of Pt3In/SiO2. The infrared results of CH3OH adsorption reveal that the substantially better performance for APR of CH3OH of Pt3InC0.5/SiO2 than Pt3In/SiO2 is due to its significantly enhanced CH bond dissociation ability. This study not only provides a straightforward and universal approach for the controlled synthesis of Ci‐PMA but also stimulates fundamental research into Ci‐PMA for catalysis and other applications.