Disclosed is a method for calculating a radio coverage in a wireless device for calculating a protective distance so as not to allow a secondary user sharing a frequency with a primary user to have an effect of radio interference on the primary user, the method including: calculating a transmission power of a wireless signal transmitted through the frequency by the secondary user; determining a region affected by the wireless signal based on the transmission power of the secondary user; calculating an average ground clearance of the determined region; calculating a height of an installation place of an antenna of the secondary user from the average ground clearance; and calculating the height of the antenna from the average ground clearance by adding a length of the antenna of the secondary user to the calculated height and calculating the radio coverage based on the height from the average ground clearance.