The invention discloses a composite heavy metal polluted soil conditioner as well as application and an application method thereof. The soil conditioner comprises the following components: plant ash, calcium magnesium phosphate, quicklime, zeolite and organic fertilizers at a weight ratio of (0.3-1.1):(0.1-1.2):(0.4-2.1):(0.1-0.6):(0.008-0.06):(0.4-1.2). Through inorganic components such as quicklime, calcium magnesium phosphate and phosphate in hydroxyapatite as well as potassium carbonate in the plant ash, the soil conditioner can be used for fixing heavy metals in polluted soil and improving the fertility of the polluted soil in combination with organic manures such as the plant ash and the organic fertilizers so as to continuously intensify the restoration of the polluted soil, has the advantages of relatively-high stability, good environmental friendliness and low cost, can be used for inactivating and restoring various heavy metal polluted soil, especially has a good restoration effect on soil pollution caused by waste slag discharged by industrial and mining enterprises, can be used for realizing the treatment goal without generating secondary pollution, and is liable to realize large-area popularization.