The invention discloses a light masonry mortar with heat insulation and preservation, comprising the following components by weight percent: 20 percent to 65 percent of portland cement, 5 percent to 50 percent of fly ashes, 0 percent to 50 percent of furnace bottom slag, 0 percent to 55 percent of slag, 10 percent to 23 percent of vitrified microspheres, 0.1 percent to 1.0 percent of water retention and thickening materials, 0.1 percent to 0.5 percent of lignocellulose and 0.1 percent to 1.0 percent of water reducing agent. The mortar has the dry density of 750 to 1000 kg / m<3>, the thermal conductivity of 0.15 to 0.20 w / m k, the lowest compressive strength of 5 Mpa and the liner shrinkage rate of less than 0.1 percent, satisfies the requirements of heat insulation and preservation of an energy-saving building, has the advantages of favorable heat insulation and preservation performance, favorable water retention, favorable workability, high adhesion strength of a wall body, simple construction, energy saving, environmental protection and the like, completely avoids the occurrence of the phenomenon of cold bridge, and efficiently prevents dry-shrinkage cracking and the phenomenon ofmoisture absorption of the wall surface.