When a homemade pryanometer was calibrated， the uncertainty of the measurement result is caused by many factors， such as the measurement reproducibility， standard instrument， temperature change， incident angle， time response， nonlinearity， zero offset， multimeter error， the operation error， spectral response error， and so on. According to 〖WTBX〗〖STBX〗JJF10591999 Evaluation and Expression of Uncertainty in Measurement〖WTBZ〗〖STBZ〗， the uncertainty evaluation for the calibration results of homemade pyranometers is conducted. The sources of uncertainty are pointed out， which obviously influence the measurement results. The uncertainty components are evaluated quantitatively. The results show that when the calibration environmental requirements are satisfied， the expanded uncertainty of the results of the pyranometer is 3.4% （〖WTBX〗k〖WTBZ〗=1.98）， in which the uncertainty component caused by the error of the incident angle is maximal. Therefore， the characteristics such as the cosine response， azimuth response， and nonlinearity of the new pyranometer should be tested to ensure the measurement accuracy.