NOVELTY - Preparing porous silicon supported three-dimensional platinum nano catalyst comprises preparing porous silicon film by dry oxygen growing silicon dioxide layer on both sides of n- silicon sheet, preparing silicon nitride layer on silicon dioxide layer, sputtering chromium/gold on silicon nitride layer, taking layer as masking layer of anode oxidation layer, wet etching masking layer and oxidizing anode; performing inductively coupled plasma and hydrogen fluoride pretreatment; and electroless plating the three dimensional platinum nanometer catalyst on surfaced modified porous silicon film.    USE - The porous silicon supported three-dimensional platinum nano catalyst is useful for producing the micro direct methanol fuel cell.    ADVANTAGE - The simple process avoids harsh processing condition and difficult quality control by using sputtering and electrochemical plating for preparing the catalyst in the conventional method.    DETAILED DESCRIPTION - Preparing porous silicon supported three-dimensional platinum nano catalyst comprises: (A) preparing the porous silicon film by (1) dry oxygen growing silicon dioxide (SiO2) layer on the both sides of the n- silicon sheet and preparing silicon nitride (Si3N4) layer on the silicon dioxide layer by using low pressure chemical vapor deposition (LPCVD), (2) sputtering chromium (Cr)/gold (Au) on the silicon nitride layer and taking the layer as the masking layer of the anode oxidation layer, (3) performing conventional photolithography of the n+ silicon sheet both sides which the Si3N2 layer of silicon sheet is sputtered with Cr/Au to form pattern, (4) wet etching the masking layer using potassium hydroxide (KOH) to form intermediate silicon film on both sides of the n+ silicon sheet and (5) oxidizing the anode to generate porous silicon; (B) performing the inductively coupled plasma (ICP) and hydrogen fluoride (HF) pretreatment which is used to realize surface modification of the porous silicon film, performing ICP etching to remove the residual silicon in the course of anode oxidation, modifying the surface of the porous silicon, and forming defect position on the surface of the porous silicon, placing porous silicon in the hydrofluoric acid (HF) water solution with concentration of 40%(v/v), and immersing for 2 seconds, then performing hydrofluoric acid solution pretreatment, forming silicon-hydrogen (Si-H) bond on the surface of porous silicon; and (C) electroless plating the three dimensional platinum nanometer catalyst on the surfaced modified porous silicon film, where the specific steps are placing the surface modified porous silicon in the water solution which the prodromal liquid is 0.5-3.5 mM of chloroplatinic acid (H2PtCl6), soaking for 30 minutes to 2 hours with temperature of 18-25 degrees C and then forming three dimensional platinum nanometer catalyst on the surface of the porous silicon.