Traditional three-dimensional (3D) imaging based on modulation degree measurement must control sinusoidal-fringe movements and synchronous focal-length changes, having a large number of shots and complex structure and control. This research proposes 3D imaging involving point matrix projection-based defocus estimation on the basis of modulation degree measurement profilometry. A point matrix with gradually changing focal length is projected onto the involved objects, and the brightness sequence of the measured surface is recorded to extract modulation information. The involved 3D information can be evaluated based on the correspondence between the maximum position and depth of the modulation sequence. This study involved analyzing the mentioned theoretical process in detail; a corresponding experimental platform was set up to verify it. The experimental results show that the proposed method can be used to accurately recover the target height. Further, compared with the traditional method, this method is structurally simpler and more convenient to control.