The invention relates to a preparation method for Mo plated on a diamond surface and a diamond/Cu composite material, belonging to the field of metal matrix composites and electronic packaging materials. The preparation method is characterized by comprising the steps of uniformly mixing diamond and MoO3 in a ratio of (1:2)-(1:4), putting the mixture into an alumina crucible, respectively placing the crucible in tube furnaces filled with hydrogen and argon for heating at the heating temperature of 900-1050 DEG C within a heat preservation time of 2-4 hours so as to complete Mo plating process; cooling the sample along with the furnace and then taking out the sample, carrying out ultrasonic cleaning on the diamond and drying, placing the diamond and Cu in a planet ball mill for uniformly mixing according to a ratio of (60:40)-(40:60)(volume%), wherein the rotation speed of the ball mill is 300r/min, and ball milling time is 120min; and finally, placing the mixture obtained by ball milling in a graphite die, and preparing the diamond/Cu composite material by adopting a discharging plasma sintering method, thereby obtaining the high-heat-conductive diamond/Cu electronic packaging material. The electronic packaging composite disclosed by the preparation method is high in the thermal conductivity and strong in repeatability.