A manufacturing method of a magnesium-aluminium spinel brick, wherein said magnesium-aluminium spinel brick comprises a flame retardant coating and a thermal insulating layer, specific manufacturing steps are as follows: preparation of flame retardant coating raw materials: contents of respective components are expressed in mass percent, sintered magnesia of granularity≤5mm 40%∼70%, fused magnesia of granularity≤3mm 10%∼40%, magnesium-aluminium spinel of granularity≤4mm 10%∼20%, 0%<corundum≤10% of granularity≤2mm are evenly mixed to prepare flame retardant coating raw material mixed powder, then 1%∼5% naphthalene binder is additionally added by taking the flame retardant coating raw material mixed powder as a basis, flame retardant coating raw materials are prepared after evenly mixing; preparation of thermal insulating layer raw materials: contents of respective components are expressed in mass percent, forsterite 40%∼60%, fayalite 10%∼40%, magnesia 10%∼50% are selected to be evenly mixed, 1%∼5% naphthalene binder is added by taking mixed powder as a basis, they are moulded by a frictional press, dried at 110°C∼150°C, burned at a high temperature above 1000°C to obtain aggregate composite hortonolite raw materials; granularity≤5mm aggregate composite hortonolite is used as a single raw material, 1%∼5% naphthalene binder is additionally added, they are evenly mixed to prepare thermal insulating layer raw materials; the above mentioned flame retardant coating raw material and thermal insulating layer raw material are spaced and loaded in a mold by using corrugated thin iron sheets, pressed into green bricks by a press machine, kept at a temperature of 110°C for 24 hours, dried, and burned into magnesium-aluminium spinel bricks at a temperature of 1550°C∼1750°C in a tunnel kiln; wherein the sequence of step and step may be inversed. preparation of flame retardant coating raw materials: contents of respective components are expressed in mass percent, sintered magnesia of granularity≤5mm 40%∼70%, fused magnesia of granularity≤3mm 10%∼40%, magnesium-aluminium spinel of granularity≤4mm 10%∼20%, 0%<corundum≤10% of granularity≤2mm are evenly mixed to prepare flame retardant coating raw material mixed powder, then 1%∼5% naphthalene binder is additionally added by taking the flame retardant coating raw material mixed powder as a basis, flame retardant coating raw materials are prepared after evenly mixing; preparation of thermal insulating layer raw materials: contents of respective components are expressed in mass percent, forsterite 40%∼60%, fayalite 10%∼40%, magnesia 10%∼50% are selected to be evenly mixed, 1%∼5% naphthalene binder is added by taking mixed powder as a basis, they are moulded by a frictional press, dried at 110°C∼150°C, burned at a high temperature above 1000°C to obtain aggregate composite hortonolite raw materials; granularity≤5mm aggregate composite hortonolite is used as a single raw material, 1%∼5% naphthalene binder is additionally added, they are evenly mixed to prepare thermal insulating layer raw materials; the above mentioned flame retardant coating raw material and thermal insulating layer raw material are spaced and loaded in a mold by using corrugated thin iron sheets, pressed into green bricks by a press machine, kept at a temperature of 110°C for 24 hours, dried, and burned into magnesium-aluminium spinel bricks at a temperature of 1550°C∼1750°C in a tunnel kiln;