Carbon nanotube (CNT) is an ideal candidate for future nanoelectronics because of its small diameter, high current-carrying capability, and high conductance in a one-dimensional nanoscale channel. The most challenging part in fabricating nanosystems could be the formation of CNT connections. Existing techniques in forming CNT connections are suffered from problems in forming a single CNT connection or not being able to precisely deposit CNTs on specific locations. One of the efficient and reliable ways to form CNT connections is to make connections between CNTs and beforehand-fabricated electrodes by using an atomic force microscopy based nanomanipulation robot, which has the ability to manipulate single CNT with nanometre precision in a controllable manner. But even this, it often happens that CNT cannot be manipulated onto the top surface of electrodes, because there are some restrict conditions among electrode thickness, CNT radius and attitude of AFM tip, this paper will study this problem in detail, some experimental results will be also presented