With increasing interconnection and interaction among the adjacent microgrids, multi-microgrid is formed. Multi-microgrid has many new characteristics, such as bi-directional power flows, flexible operation modes and different control strategy of inverter interfaced distributed generations (IIDGs), which challenge multi-microgrid protection. Based on the voltage and current distribution characteristics of the line parameters, this paper proposes a new protection scheme for internal tie lines fault of multi-microgrid, which takes the change of measured bus admittance as the criterion. First, measured admittance amplitude of both ends of tie lines, before and after the fault are calculated. Then, comparing the admittance amplitude to select the likely faulty lines. Finally, fault line is located on comparison the phase of measured admittance among the likely faulty lines. This scheme with high sensitivity and reliability, has a simple principle and is easy to be adjusted. PSCAD/EMTDC is used in simulation analysis, and simulation results have verified the correctness and effectiveness of the protection scheme.