A composite autofocusing technique consisting of coarse autofocusing and fine autofocusing is proposed for test system of optical-lens parameter. In the coarse autofocusing procedure, variance function achieved from the whole image is selected as sharpness evaluation function, mean comparison method is applied to realize the hill-climbing algorithm for focal plane searching, and a 3-point method is used to initialize the searching direction. In the fine autofocusing procedure, a conditional dilation method based on mathematical morphology and a shape factor are employed to extract the connected regions, namely, the target images. Brenner function within the target image is selected as the sharpness evaluation function, and the hill-climbing algorithm with single-point comparison is used to find the focal plane accurately. The experiments validate that the composite autofocusing technique possesses not only high accuracy but also large autofocusing range. It can guarantee that the focusing position locates in the depth of field of the camera lens and the lens parameter measuring results possess good accuracy and repeatability.