The invention relates to a filler for a composite pipe fitting, in particular to a formula of filling concrete for the composite pipe fitting. The coating is characterized by comprising adaptive metal powder, lead powder, calcium carbonate powder, cement, an organic binder, an antirust agent, a thickening agent, an anti-slip agent and water. The matching ratio of the adaptive metal powder, the lead powder, the calcium carbonate powder, the cement, the organic binding agent, the antirust agent, the thickening agent, the anti-slip agent and the water is as follows in parts by mass: 45 to 62 parts of the adaptive metal powder, 10 to 28 parts of the lead powder, 5 to 13 parts of the calcium carbonate powder, 20 to 36 parts of the cement, 5 to 13 parts of the organic binding agent, 3 to 6.5 parts of the antirust agent, 0.03 to 0.07 part of the thickening agent, 0.05 to 0.15 part of the anti-slip agent and 20 to 33 parts of the water; the sealing performance and the service life of the composite pipe fitting can be stably kept for a long time, smoothness of a water conveying pipeline is guaranteed, potential safety hazards are reduced, the pipeline maintenance cost is reduced, the water conveying efficiency is improved, and the beneficial effects of reducing environmental pollution and saving energy are achieved.