By taking optical acquiring 3D objects with a lens array for an example, a method to obtain the optimal pick-up distance was proposed to reduce the elemental image overlap and the crosstalk in reconstructed three-dimensional images for 3D integral imaging and display technology. By analyzing the effective imaging rates of object points and the image point utilization of objects with various sizes at different pick-up distances, the optimal pick-up distance was achieved. Compared with conventional methods for a specific integral imaging system, the product of the effective imaging rates of object points and image point utilization has increased at the optimal pick-up distance and the maximum one can increased by 34 times. Optical experimental results show that the reconstructed images has full 3D information and wealth detail, which verifies the feasibility of the proposed method. Moreover, the method is suitable for both the lens array and the camera array to acquire 3D information.