Recently, the matter of excessive cooling load in buildings is being occurred in summer. This problem is mainly due to uncontrolled solar radiation transmitted to building envelope. To control transmitted solar radiation, shading devices are generally used in buildings. Among shading devices, venetian blind has the advantage to adjust indoor comfort and visual comfort by slat angle control. This paper is focused on comparisons of calculation methods for solar transmittance, which is used in EnergyPlus and DIN EN 13363-2 for thermal simulation of venetian blind combined with glazing. Generally, total solar transmittance is calculated through correlations of glazing transmittance and venetian blind transmittance. EnergyPlus considers angular dependance for calculating glazing transmittance, and it uses Radiosity Method for blind transmittance calculation. However, DIN EN 13363-2 assumed normal incident angle for glazing transmittance and it uses different method for calculating blind transmittance, which is more simplified than EnergyPlus. Consequently, EnergyPlus algorithms demand more detailed information than DIN EN 13363-2 to calculate solar transmittance of glazing system. Furthermore, EnergyPlus always had higher blind transmittance than that of DIN EN 13363-2, due to consider of inner reflection for venetian blind, However, DIN EN 13363-2 always had higher glazing transmittance than EnergyPlus, because it assumed normal incident angle. As a result, they show similar results for total solar transmittance of glazing system.