The Unified Power Flow Controller (UPFC) is one of the Flexible AC Transmission System (FACTS) devices used in transmission line for real-time control and dynamic compensation. The converter and DC side have complicated fault characteristics, the effect of fault is an inevitable issue. This paper first introduces the basic structure and operating principle of MMC-UPFC, next analyzes fault characteristics of several typical converter side and DC side fault. According to the analysis, the protection scheme for MMC-UPFC converter and DC side is proposed. Moreover, aiming at the problem that conventional differential protection for converter arm single-phase-to-ground fault and DC side single-pole-to-ground fault cannot meet the requirement of reliability, an improved protection scheme is proposed. Simulation results based on Real-Time Digital Simulator (RTDS) verify the proposed protection scheme. This work is supported by Science and Technology Project of State Grid Jiangsu Electric Power Company (No. J2017041).