Through using focusing capillary, the extreme ultraviolet (EUV) light source of collimator is channelled out of flange, and the light beam′s divergence angle is controlled to match the collimator′s aperture angle. This article analyzes and calculates the case of directly using a light source to illuminate target disk and the light beam cannot cover the diameter of the effective primary mirror. Focusing capillary can make the light beam cover the aperture angle of collimator and the two states of the EUV collimator with and without capillary are tested.The results show that using focusing capillary can expand light beam′s divergence angle. Besides, the maximum number of photons without capillary is close to 1×105 and the maximum number of photons with capillary can reach 1×104. The testing data show that the EUV focusing capillary′s transmission efficiency can achieve 10% to meet technical index of EUV collimator.