A precision method for measuring accurately the core pitch of fiber array (FA) is reported，which can be broadly used in optical communication systems and distributed fiber sensor network.The measurement system mainly consists of a white light source，a precision stage，a microscope，a CCD and a computer.The image comprising at least two fiber cores is acquired.The edge of the fiber core is extracted at sub-pixel level through quadric polynomial interpolation method and the center is located through least square method.Experimental results indicate that，the fiber pitch can be measured with a resolution of 16nm and a standard deviation of 23nm.This method can realize the automation，non-contact，high precision measurement of fiber array spacing.