The invention discloses a composite heavy metal polluted soil in-situ fixing method. The method comprises the following steps of: preparing a heavy metal polluted soil restoration agent by using 80 to 90 weight parts of bentonite or kaolin serving as a filling agent, 0.5 to 15 weight parts of ferrous sulfide, 0.5 to 5 weight parts of magnesium sulfate, 1.5 to 8 weight parts of magnesium sulfite, 1 to 5 weight parts of magnesium oxide, 2 to 10 weight parts of calcium hydroxide and 1 to 5 weight parts of phosphorus-containing preparation; and mixing the components and heavy metal polluted soil according to the weight ratio of 1:(5-20), and uniformly stirring to make the humidity of the soil kept between 15 and 30 percent, wherein heavy metal ions in the polluted soil are converted into water-insoluble metal sulfides, hydroxides, multi-metal co-precipitates, basic carbonates and phosphate minerals, the biological activity of heavy metal is lost, and the heavy metal is fixed in the soil. The restored soil meets the requirement of second-level standard values of 'Environmental Quality Standard for Soil' (GB 15618-1995) in China.