With the increasing penetration of photovoltaic in distribution network, the research on the fault characteristics of photovoltaic is particularly important for the protection and control of distribution network. By establishing the transient model of distributed photovoltaic generator, the power characteristics of distributed photovoltaic generator under the fault condition are analyzed and the equation of electromagnetic transient current is given. A control-in-the-loop simulation system based on an actual photovoltaic controller is built on the RTDS simulation platform. Through this platform, it verifies the transient process of the unipolar photovoltaic generator with low voltage ride through capability in different fault conditions. The current harmonic characteristics of the distributed photovoltaic generator are also analyzed under asymmetric faults. The fault characteristics of photovoltaic are comprehensively expounded through theoretical analysis and experimental verification, which provides a reference for the calculation of fault current and the protection setting of photovoltaic access to distribution network. This work is supported by National Key Research and Development Program of China (No. 2017YFB0902900) and Science and Technology Project of State Grid Anhui Electric Power Co., Ltd. (No. 52120017001G).