Method for detecting interference in radar system and radar using the same are disclosed. Aiming to the radar, a method for ensuring the interference levels from an object, a back wave of a radar wave emitted by the radar and a radio wave emitted by other radars and a radar are provided, in particular a frequency modulation continuous wave (FMCW) radar, which executes the method for ensuring the interference level between the radar and other radars. According to the method of the invention, after the frequency spectrum characteristics of the incident radio wave is obtained by performing frequency analysis to the incident radio wave received by the radar, one of the frequency components of the incident radio wave, that is, the frequency component with higher intensity than a pre-determined intensity threshold in the frequency components is not used for computing an reference value representing the interference level.