Depth extraction systems with multiple light-coding depth cameras (LCDCs) have been widely used in the field of three-dimensional reconstruction in recent years. However, interference among the depth cameras would significantly deteriorate the quality of depth images and thus limit their efficiency in various applications. In this paper, we first establish the linear illumination model of multiple LCDCs to study the property of interference. Since the interference-free pattern is hard to distinguish from the interfered pattern, we present an interference reduction scheme based on pattern modulation and demodulation to address this problem. Projected patterns from the LCDCs are then uniformly modulated using a coefficient matrix. Afterwards, we further put forward an interference-alignment-based solution to demodulate the captured image frames, thereby fast recovering the interference-free pattern of a single LCDC. Depth images can finally be generated based on the recovered interference-free pattern. Experimental results from simulated and real-world examples show that the proposed scheme can effectively reduce the impact of interference and improve the quality of depth images.