The invention relates to a method for producing a low-platinum alloy shell-core structure catalyst by means of liquid phase system reduction of H2, in particular to a nano-alloy catalyst with a non-noble metal core coated by a Pt alloy shell. The method for producing the low-platinum alloy shell-core structure catalyst by means of liquid phase system reduction of H2 comprises the following steps:(1) dispersing and loading a non-noble metal precursor; (2) reducing and supporting a non-noble metal core; (3) conducting replacement and coating by means of a transition noble metal shell; (4) underthe reducing action of H2, reducing a noble metal alloy shell, and conducting coating by means of the noble metal alloy shell; (5) conducting crystal ageing and growing; and (6) conducting centrifugation and drying to obtain the low-platinum shell-core alloy catalyst. The obtained nanometer core-shell alloy catalyst with the non-noble metal core coated by Pt and the Pt alloy shell is in a form ofultrafine nanoparticles, has efficient oxygen reduction activity, is low in catalyst loading capacity and good in activity and stability, and has important application values in the fields of fuel cells and electrochemical oxygen reduction catalysis processes.