Different neutral point grounding modes have their own advantages and disadvantages，and the decision making of neutral point grounding mode for medium voltage distribution network needs to consider the power supply reliability，overvoltage and insulation coordination，relay protection，communication system interference，electrical safety and grounding device，which relate to the electric network reliability，security and economy movement aspect.A neutral point grounding mode decision method which comprehensively considers the reliability，safety and economy factors is proposed.The method combines the reliability evaluation，safety protection，construction and operation cost with the realization of distribution network for different neutral point grounding modes，and makes the optimal decision of neutral point grounding mode by calculating life cycle cost of different neutral grounding modes and coordinating the reliability index.An example is used to verify the feasibility and effectiveness of the decision method.