讨论了一种新型的孔径测量方法双弦法，建立了测量模型，指出传统的转折点法、对称点法是其特例。若ｌ１，ｌ２分布在孔两侧，合理选择Ｈ／Ｄ，可以减小扫描误差的影响。最后讨论了利用双弦法对工件进行Ｚ向微米级定位。根据此原理，很容易实现精密孔径测量仪器的智能化、高准确度和高效率。 This paper discusses a new method of double-line method of aperture measurement, establishes the measurement model, points out the traditional turning point method, and the symmetry point method is its special case. If l1, l2 distributed in both sides of the hole, a reasonable choice of H / D, you can reduce the impact of scanning errors. Finally, the use of double-string method to the workpiece Z-micron positioning. According to this principle, it is easy to realize the precision, high accuracy and high efficiency of the precision aperture measuring instrument.