The invention discloses a thermal-insulation mortar for masonry, which is prepared from the following raw materials in parts by weight: 40-50 parts of ferrous aluminate cement, 25-35 parts of haydite sand, 10-15 parts of coal slag powder, 5-10 parts of magnesia, 8-12 parts of pyrauxite powder, 10-15 parts of floating bead, 0.5-1.5 parts of sodium fluosilicate, 2-3 parts of redispersible latex powder, 3-5 parts of nano titanium dioxide, 1.5-2.5 parts of cellulose acetate, 2-4 parts of wood dust, 4-8 parts of magnesium hydroxide, 1-2 parts of sodium carboxymethyl starch and 3-6 parts of composite filler. The thermal-insulation mortar for masonry has similar drying shrinkage deformation and heat-conducting property to the light-weight building block, can effectively avoid the occurrence of the cold bridge phenomenon, has the advantages of excellent workability, excellent binding strength, excellent flowability, excellent water retention property, excellent compression strength, excellent crack resistance, no shedding, no cracking, no molding, high stability, favorable workability and the like, is convenient to use, and has huge market prospects.