NOVELTY - A catalyst sizing agent of non-supported type fuel cell comprises metal nanoparticle, proton-conducting polymer, and aqueous alcohol solution. The aqueous alcohol solution is 50-99.9% of the whole sizing agent. The water is 0.01-50% of the aqueous alcohol solution. The metal nanoparticles are modified in situ by proton-conducting polymer. The mass ratio of polymer to metal nanoparticle is 0.02-1:1.    USE - A catalyst sizing agent of non-supported type fuel cell.    ADVANTAGE - During preparation of catalyst, the proton-conducting polymer provided as protective agent is added in little amount. After purification, the reaction product can be directly used for preparing catalyst layer of fuel cell without adding or removing proton-conducting polymer. The average particle diameter of catalyst is 2-3 mm. The obtained catalyst is applied in fuel cell, realizing good cell performance.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for preparation of catalyst sizing agent, comprising:    (A) placing mixed solution of proton-conducting polymer with mass density of 1-20% into aqueous ethanol solution, where polymer is protective agent of metal;    (B) adding soluble salt solution precursor with mass density of 0.1-20% and metal active component of catalyst contained in solution, uniformly stirring solution, adding alkaline pH adjusting solution with pH value of 8-13 and reducer into solution, stirring and refluxing at 60-100 degrees C for 1-60 minutes; and    (C) dialyzing obtained solution in aqueous ethanol solution to remove impurity ion and organic by-product and obtain catalyst sizing agent.    The mass ratio of mixed solution of proton conducting polymer to aqueous ethanol solution is 0.001:1. The mass ratio of proton conducting polymer to metal is 0.02-1:1. The mass ratio of reducer to metal is 1-500:1. The pH value is controlled at 8-13 during the reaction to obtain solution of metal nanoparticle modified by proton conducting polymer. The retention molecule of dialysis bag is 1 k-100 kDa. The mass percentage of water in aqueous ethanol solution is 0.01-50%.