Based on the modular multilevel converter high voltage direct current（MMC-HVDC）system，a piecewise analytical formula method for valve loss calculation of converters is proposed.Firstly，the arm voltage is transformed into a smooth waveform after removing the nearest integer function.Under this simplification，the conduction losses can be precisely generalized as piecewise analytical formulas right at the instant the arm current crosses zero.Secondly，the switching losses are divided into two parts:the essential switching losses and the additional switching losses.As a result of the introduction of the changing rate function，the essential switching losses are also generalized as piecewise analytical formulas.For the additional switching losses，a method is adopted to estimate the value.The procedures of the proposed methodology for valve loss evaluation of MMC-HVDC are given.Finally，case studies have been carried out based on a 300 MW/±150 kV MMC-HVDC.The results show that the proposed methodology is efficient and effective.