In order to optimize the heat preservation capacity of Chinese solar greenhouse (CSG) and further reduce energy consumption, we clarified the mechanism of the external thermal insulation layer that affecting the microclimate environment of CSG. The most excellent thickness of the external insulation layer of the solar greenhouse envelope structure in high latitude and cold region has been indicated. A three-dimensional mathematical model was developed based on computational fluid dynamics (CFD) and verified using experimental measurement. The temperature variations, heat variations and economic benefit were analyzed. The results indicated that covering the outer surface of the enclosures with a thermal insulation layer could effectively increase the greenhouse temperature by 1.2~4.0°C. SW had the lowest unit cost (USD 282.52/°C), but it limited the increase in greenhouse air temperature. Covering the outer surface of the north wall with insulation layer has better profitability and higher cost performance than that of the side wall and the north roof. During the construction of the greenhouse in high latitude and cold region, CC as the optimal solution could raise the greenhouse air temperature maximally. The optimal thickness of the external insulation layer of each maintenance structure is obtained as follows: north wall 80 mm, side wall 80 mm, north roof 100 mm.