The theory derive of five-step method for position measurement of zero light path difference in white light interferer system was described.The local modulation of fringes was gotten under the condition of one fourth of interferer fringes period length as the sampling interval and the light intensity at five points be measured nearby as the basic data.The centrobaric method was used to determine the position with the maximum modulation value of fringes and the position was used as the point of zero light path difference.In theory,the analog data derived from different formulae of interfere intensity were analyzed and the effect of mechanical precision and opto-electronical measurement anchor point precision in the measurement system was also calculated.Under this calculation,the maximum errors of this measuring method is less than 1/4 cneter wave length of interferer light.