The invention discloses a cement mortar and a preparation method thereof. The cement mortar is prepared from the following raw materials in parts by weight: 50-100 parts of cement, 10-50 parts of zinc sulfide, 55-65 parts of urea-formaldehyde resin, 45-55 parts of sodium chloride, 20-30 parts of hydroxymethyl cellulose, 40-80 parts of diethylene glycol, 100-120 parts of calcium carbonate, 10-50 parts of antimony trioxide, 40-50 parts of chlorinated paraffin, 70-80 parts of methylethylketone, 80-120 parts of porcelain clay powder, 20-30 parts of curing agent and 100-120 parts of water. The preparation method comprises the following steps: uniformly mixing the cement, zinc sulfide, urea-formaldehyde resin, sodium chloride, hydroxymethyl cellulose, diethylene glycol and water, heating to 200-220 DEG C, stirring for 50-70 seconds, adding the calcium carbonate, antimony trioxide, chlorinated paraffin, methylethylketone, porcelain clay powder and curing agent, and uniformly mixing. The cement mortar has the advantages of low bleeding rate (only 0.2-0.3%), high seepage resistance and high freezing resistance.