The invention relates to low-strength composite mortar doped with glass bead aggregate and a chemical fiber and a preparation method thereof, and belongs to the field of a building material. The mortar comprises glass beads, fine sand, cement, lime putty, a chemical fiber and water, wherein the mixed aggregate is a mixture of the glass beads and the natural fine sand; the glass beads account for 70-85% of the weight; the cement is ordinary portland cement; the glass beads adopt renewable glass beads of taking broken glass and the like as raw materials; the glass beads of which the diameters are 3.5-5mm are high in strength and good in durability; the fine sand is natural sand, the maximal particle size can pass through a sieve hole of 1.5mm; the chemical fiber comprises a fiber-reinforced plastic (FRP) fiber, a polyester fiber, a polyamide fiber, a polyacrylonitrile fiber, and a natural chemical fiber with good flexibility and block property; the lime putty is a product of the limestone after being cured. The low-strength composite mortar has the advantages of being low in cost, environment-friendly and available in materials, wide in distribution, and less in energy consumption, and meanwhile, the motor is simple in operation method and easy to construct.