The invention discloses a defect detection system for an extreme ultraviolet lithography mask. The defect detection system for the extreme ultraviolet lithography mask comprises an extreme ultraviolet light source, an extreme ultraviolet light transmission system (comprising a multilayer plane mirror and a multilayer concave condenser), an extreme ultraviolet lithography mask, a sample scan stage, a photon sieve, a CCD camera, a PC, an vibration isolation platform, a vacuum chamber and a multilayer half-transparent half-reflecting mirror. In the defect detection system for the extreme ultraviolet lithography mask, a conventional Schwarzchild lens is replaced by the photon sieve, so that imaging of the mask by an extreme ultraviolet band is realized, and thus defects on the mask are detected. Due to the fact of replacement of the conventional Schwarzchild lens which is difficult to process, high in cost and large in volume by the photon sieve which has the characteristics of small volume, good workability, low cost and high resolution ratio, the defect detection system for the extreme ultraviolet lithography mask is realized in lower cost, smaller volume and high resolution ratio.