The invention relates to a PVC (polyvinyl chloride) heat stabilizer and a preparation method thereof, in particular relates to an environmental-friendly composite organic tin heat stabilizer and a preparation method thereof. The environmental-friendly composite organic tin heat stabilizer is prepared from at least the following components in parts by weight: 20-80 parts of an organic tin compound,10-50 parts of a zinc-based stabilizer, 1-10 parts of a phosphite compound, 1-10 parts of hydrotalcite and 1-10 parts of a lubricant.