A kind of form stable phase change material（PCM） based on capric lauric acid eutectic acting as the heat absorbing material and nano silicon dioxide serving as the supportive material was prepared by sol gel method. The morphology, chemical characteristics and thermal properties of the composite PCM were investigated by transmission electron microscopy（TEM）, scanning electron microscopy（SEM）, and Fourier transform infrared（FT IR）, differential scanning calorimetry（DSC） and thermogravimetric analysis（TGA）. The results indicate that fatty acid eutectic can be immobilized in the three dimensional network structure when the composite PCM is heated to above the phase change temperature. The proportion of the CA LA eutectic in the composite PCM is 46%(by mass). The phase change temperature and latent heat of the composite PCM were determined as 19.57℃ and 71.28J/g, respectively. Mean while, thermal conductivity of the composite was measured to be 0.178W/（m·K） by using the transient hot wire method. Thus it can be applied for energy conservation as the thermal insulation material.