A method of calibrating a 3D (three dimensional) camera , comprising: pre-calibrating a 2D (two dimensional) camera coordinate system (C), and arranging the 3D camera to be calibrated in a proximity to a 2D camera ; arranging in a common field of view of the 3D camera and the 2D camera a 3D object and a background having color contrast on surfaces between each other; controlling the 2D camera to capture an image, and controlling the 3D camera to capture a point cloud; separating a point cloud of the 3D object and a point cloud of the background captured by the 3D camera , and recording raw colors of the point cloud of the 3D object and raw colors of the point cloud of the background ; transforming the point cloud of the 3D object and the point cloud of the background into coordinates in the 2D camera coordinate system (C) using a default value of a predetermined transform parameter; obtaining a transformed color of each point in the point clouds at a position of the 3D object or the background in the image captured by of the 2D camera according to each point of the transformed point cloud of the 3D object , or from positions of the background in the image captured by the 2D camera according to each point of the transformed point cloud of the background ; comparing the raw color and the transformed color of each point in the point cloud of the 3D object and in the point cloud of the background to compute a missing score of the point cloud of the 3D object and the point cloud of the background ; and determining whether the missing score is less than a predetermined threshold, and if so, determining that a transform mapping from a coordinate system (T) of the 3D camera to the 2D camera coordinate system (C) is completed. pre-calibrating a 2D (two dimensional) camera coordinate system (C), and arranging the 3D camera to be calibrated in a proximity to a 2D camera ; arranging in a common field of view of the 3D camera and the 2D camera a 3D object and a background having color contrast on surfaces between each other; controlling the 2D camera to capture an image, and controlling the 3D camera to capture a point cloud; separating a point cloud of the 3D object and a point cloud of the background captured by the 3D camera , and recording raw colors of the point cloud of the 3D object and raw colors of the point cloud of the background ; transforming the point cloud of the 3D object and the point cloud of the background into coordinates in the 2D camera coordinate system (C) using a default value of a predetermined transform parameter; obtaining a transformed color of each point in the point clouds at a position of the 3D object or the background in the image captured by of the 2D camera according to each point of the transformed point cloud of the 3D object , or from positions of the background in the image captured by the 2D camera according to each point of the transformed point cloud of the background ; comparing the raw color and the transformed color of each point in the point cloud of the 3D object and in the point cloud of the background to compute a missing score of the point cloud of the 3D object and the point cloud of the background ; and determining whether the missing score is less than a predetermined threshold, and if so, determining that a transform mapping from a coordinate system (T) of the 3D camera to the 2D camera coordinate system (C) is completed. <EOS>