Focusing on the rapidly developing non-contact measurement method of morphology restoration technology, this study explores its wide application in measuring small components. The subject of measurement is the secondary nozzle of an engine fuel injector assembly. Sequential images of the inner hole at the inlet of the secondary nozzle are collected at equal intervals. An improved variance function is employed to extract three-dimensional point cloud data, with experimental validation showing that the optimal clarity evaluation window size is 22*22. By slicing the point cloud, the three-dimensional sections are converted into two-dimensional images, and parameters of the inner hole circle are obtained through edge extraction and Hough transformation. Ultimately, the cone angle and taper size of the fuel injector inlet hole are calculated. Experimental results demonstrate a relative error of 3.45% for the outlet inner diameter and a relative error of 4.11% for taper measurement. The findings provide accurate testing data for enhancing the machining precision and quality of fuel injectors, offering references for optimizing their manufacturing processes.