Li2OAl2O3SiO2 system transparent glass was prepared by melting method, and ultralow expansion glassceramics were obtained by heat treatment with TiO2, ZrO2 and P2O5 as composite nucleating agents. The effects of heat treatment parameters on thermal expansion coefficient of glassceramics were studied by orthogonal experiments. The optimal heat treatment parameters were obtained through calculation and analysis, that is, the nucleation temperature is 600 ℃, the nucleation time is 3 h, the crystallization temperature is 820 ℃, and the crystallization time is 5 h. The main crystalline phase of glassceramics obtained under this heat treatment process is βquartz solid solution, and the thermal expansion coefficient is 1.6×10-8 ℃-1. The crystallization and microstructure of glassceramics were studied by means of differential thermal analysis, Xray diffraction analysis, scanning electron microscopy analysis and transmission electron microscopy analysis. The relationship between heat treatment process, thermal expansion properties and microstructure of glassceramics was analyzed. The results show that the thermal expansion coefficient of glassceramics is determined by the type and content of crystalline phase, and the size and content of crystalline phase which formed inside glassceramics are closely related to heat treatment process.