The invention relates to a vegetable soft capsule shell composition and a preparation method thereof. The composition comprises the following ingredients by content: 0-30% of hydroxypropyl starch, 0-20% of hydroxypropyl methyl cellulose, 0-20% of pullulan, 0.1-10% of one or more gels, 0.5-30% of one or more plasticizers, 0-5% of one or more soluble salts, 0-4% of an opacifier, 0-4% of one or more colorants and 10-90% of water, wherein the contents of hydroxypropyl starch, hydroxypropyl methyl cellulose and pullulan are not zero, and the total content is 100%. The preparation method comprises the following steps: adding hydroxypropyl starch into water for dispersion, so as to obtain a solution A; adding other ingredients except hydroxypropyl methyl cellulose into water for dispersion, so as to obtain a solution B; mixing the solution A with the solution B, heating to 90-95 DEG C, carrying out stirring and heat preservation for 0.5-2 hours, cooling to 75-80 DEG C, and carrying out heat preservation, still standing and defoaming to obtain a glue solution; measuring the viscosity of the glue solution after defoaming, wherein the composition is obtained when the viscosity reaches 20,000-30,000 mPa.s.