The invention relates to a method for preparing ultrafine platinum powder by adopting liquid-phase reduction. The method comprises the following steps: preparing platinum salt solution, and regulating the pH value of the platinum salt solution to be 2-7, dropwise adding the obtained platinum salt solution into mixed solution of a reducing solution and a dispersing agent while mixing, continuing to mix for reaction for 10-30 min after dropwise adding the platinum salt solution, and obtaining ultrafine platinum powder after filtering, washing and drying products generated by reaction, wherein the dispersing agent is aqueous solution of any one or combination of ethylene glycol, glycerin, polyvinyl alcohol and isobutyl alcohol, and the reducing solution is alkaline aqueous solution of any one or combination of formaldehyde, hydrazine hydrate, ascorbic acid, oxalic acid and sodium borohydride. The ultrafine platinum powder prepared by the method has the characteristics of high purity, small particle size, uniform spherical structure, good dispersibility and the like, and can be applied in conductive components of conductive paste and electrode paste with high stability, high reliability and good performance in microelectronic technology.