As the ability of DC circuit breaker is limited, transmission line protection has to identify the fault and inform the DC circuit breaker to cut off fault current as quickly as possible after a fault occurs on the transmission line of modular multilevel converter-based high-voltage direct current (MMC-HVDC) grid, in order to prevent the fault current from exceeding the ability of the DC circuit breaker. MMC-HVDC grid requires the speed of transmission line protection to be extremely fast. Travelling wave protection utilises the fault-induced travelling waves to construct protection criteria. As fault information firstly propagates in the form of travelling waves in the grid after a fault, travelling wave protection can achieve the fastest operation speed in theory, so it is an ideal choice for MMC-HVDC grid. This study analyses the characteristics of fault-induced travelling waves in the MMC-HVDC grid and the results can be the foundation of travelling wave protection of transmission line in MMC-HVDC grid.