Different from the traditional isotropic insulation design which aims at reducing building heat loss, a new anisotropic insulation design method which fully considers the orientation difference of solar irradiation is proposed for the purpose of reducing indoor radiant thermal discomfort. Based on the principle of equal heat flux intensity of the envelope, a simplified calculation method of the insulation thickness in each orientation is established. The relationship between each orientation insulation thickness can be simplified as a linear relationship. The influence characteristics between the factors like exterior surface, brick wall thickness, brick and insulation material and the orientation differential insulation thickness are obtained. Six typical cities in China are selected in combination with solar energy resource zones and building thermal divisions, and the insulation thickness of building envelope in each region is calculated. The results show that the orientation differential insulation design mode is suitable for solar energy resource zone I and zone II. Taking Lhasa as an example, compared with isotropic thermal insulation conditions, the material cost of thermal insulation layer under orientation differential insulation conditions is reduced by 24.6%, and the average heating energy consumption increases only by 6.1%. When the insulation material is the same, the average heating energy consumption can be reduced by 9.0%. The results can provide a reliable basis for the application of orientation differential insulation technology in rich areas of solar energy resource.