An object detection method with a rising classifier effect is embedded in an object detection device and has steps of acquiring image information; determining a position of an obstacle in the image information, wherein the image information is detected for generation of an extracted range corresponding to the obstacle; recognizing an extracted contour of the obstacle, wherein the extracted contour of the obstacle associated with the extracted range is obtained by using an algorithm for Poisson gradient vector flow based active deformable contour model and a multi-mesh algorithm with different grid sizes; and forming a maximum border of the extracted contour of the obstacle for a classifier to recognize a type of the obstacle according to the maximum border of the obstacle. Accordingly, the object detection method is advantageous in complete extraction, higher recognition rate, faster computation and feasibility to be integrated with vehicle systems.