The invention discloses a look-up table interpolation-based photovoltaic array fault diagnosing and positioning method which comprises the following steps: data in a normal operating state in all kinds of weather is chosen as original data based on different seasons; two two-dimensional tables that are respectively related to current and voltage are formed, reference current and voltage values are obtained via use of spline interpolation based on real time temperature and irradiation data look-up tables, and the reference current and voltage values are used as reference for determining a fault degree; abnormal current and voltage values is chosen among all strings of real time current and voltage values and a string number of an abnormal string is obtained, a fault degree of the string with the abnormal values is determined, and the fault degree is determined based on deviation of abnormal current and voltage values from reference current and voltage values. The beneficial effects of the photovoltaic array fault diagnosing and positioning method are that fault current and voltage values can be accurately extracted in real time, a corresponding string can be positioned, real time fault diagnosing and positioning of photovoltaic arrays can be realized, and current and voltage faults and corresponding fault degrees can be determined; the photovoltaic array fault diagnosing and positioning method is high in adaptability and speed and excellent in actual effect.