Porous mullite lightweight materials were prepared by a microemulsion template method and subsequent sintering with fly ash and calcined bauxite as raw materials, Isobam 104 as a dispersant, carboxymethyl cellulose as a suspending agent, polyoxyethylene sorbitan monooleate (Tween 80) as a surfactant, isooctane as an oil phase, ethylene glycol glycidyl ether as a binder and tetraethylenepentamine as a curing agent. The influences of fly ash content and Tween 80 content on the phase composition, linear shrinkage, bulk density, porosity, microstructure and mechanical properties of porous mullite lightweight materials were investigated. The results show that the linear shrinkage rate, bulk density and mechanical strength of porous materials prepared with 55% fly ash decrease, but the porosity increases as the volume ratio of Tween 80 to water increases from 2:100 to 5:100. When the volume ratio of Tween 80 to water is 5:100, the compressive strength and flexural strength of porous mullite lightweight materials with a porosity of 65.5%, a spherical pore diameter of 162 μm, and a linear shrinkage rate of only 14.5% can reach 42.5 MPa and 26.0 MPa, respectively.