Abstract: To eliminate the possibility of colliding with other wells in cluster wells, preliminary research has been performed to determine a ranging calculation method to avoid collision with adjacent wells using ranging electromagnetic surveying while drilling tools. Based on structure and fundamental principles of such electromagnetic tools, the magnetic source was regarded as a magnetic dipole to determine the distribution of magnetic fields around the magnetic source in accordance with the magnetic dipole theory. In this way, models for calculation of magnetic fields around the adjacent casing and intensity of magnetic induction around probe. In addition, the ranging calculation method of anti-collision while drilling by using electromagnetic anti-collision tools was established. Numerical simulation and other methods were adopted to determine the impact of parameters such as the magnetic source spacing inside the probe, the magnetic moment of magnetic source, the relative permeability of the casing, the diameter of casing, and the included angle between the drilling well and the adjacent well. It also included the magnetic induction intensity around the probe (positively correlated to spacing between sources), magnetic moments, relatively magnetic conductivity and diameter of casing, and other parameters. The proper design of key parameters of such tools could effectively enhance the intensity of magnetic induction around the probe and promote the accuracy of such tools. Research results showed that the newly developed ranging methods for avoiding colliding with adjacent wells while drilling by using electromagnetic tools could be used to determine the spacing and azimuth between the well being drilled and adjacent well in real time. These tools could basically satisfy demands for the drilling of cluster wells and may have great significance in the development of such anti-collision surveying tools.