A depth-sensing device and its method are provided. The depth-sensing device includes a projection device, an image capture device, and an image processing device. The projection device projects a first projection pattern to a field at a first time and projects a second projection pattern to the same field at a second time. The density of the first projection pattern is lower than the density of the second projection pattern. The image capture device captures the first projection pattern projected to the field at the first time to obtain a first image and captures the second projection pattern projected to the field at the second time to obtain a second image. The image processing device processes the first and second images to obtain two depth maps and at least merges the depth maps to generate a final depth map of the field.