NOVELTY - A sulfate/tin oxide/metal oxide (SO42-/SnO2-M2O3) solid super acid catalyst is prepared by dissolving soluble tin (Sn) salt, soluble gallium (Ga) salt, soluble aluminum (Al) salt or soluble iron (Fe) salt into water; dripping ammonia under stirring condition until pH is 8-9, and aging for 1-3 hours at room temperature; separating deposit, washing with ammonium acetate solution, and drying filter cake at 80-110 degrees C; soaking with sulfuric acid for 0.5-2 hours, filtering, and drying filter cake at 80-110 degrees C; and roasting at 400-600 degrees C for 2-4 hours in air to obtain desired catalyst.    USE - Method for preparing sulfate/tin oxide/metal oxide (SO42-/SnO2-M2O3) solid super acid catalyst (claimed) for esterifying and synthesizing biodiesel oil.    ADVANTAGE - The prepared catalyst provides high esterifying rate and moderate reaction condition.    DETAILED DESCRIPTION - The SO42-/SnO2-M2O3 solid super acid catalyst is prepared by:    (A) dissolving soluble Sn salt, soluble Ga salt, soluble Al salt or soluble Fe salt into water so that metal ion concentration of Sn, Ga, Al and Fe is 0.2-1.0 mol/L;    (B) dripping ammonia under stirring condition until pH is 8-9, aging for 1-3 hours at room temperature, where mol ratio of Ga, Al or Fe and Sn is 0.002:1-0.15:1;    (C) centrifugal separating prepared deposit, washing with ammonium acetate solution (1-6 wt.%), and drying filter cake at 80-110 degrees C for 12-36 hours; soaking with sulfuric acid (2-4 mol/L) for 0.5-2 hours, filtering, and drying filter cake at 80-110 degrees C for 12-36 hours; and    (D) roasting at 400-600 degrees C for 2-4 hours in air to obtain SO42-/SnO2-M2O3 solid super acid catalyst.    M=Ga, Al or Fe.    An INDEPENDENT CLAIM is included for a use of the SO42-/SnO2-M2O3 solid super acid catalyst activating catalyst in air at 60-200 degrees C for 12-24 hours before reaction; and catalyzing dilaurate esterified with methanol inside intermittent reaction kettle at normal pressure, where catalytic temperature is 50-70 degrees C, reaction time is 1-6 hours, mol ratio of dilaurate and methanol is 15:1, and amount of catalyst accounts for 1-3 wt.% of total material weight.