A built-in S-typed array eddy current testing probe and a method for detecting defects of a tubular structure are provided. The probe includes an exciting coil part and a plurality of pick-up coil parts, wherein: the exciting coil part includes multiple bundles of exciting coil wires helically wound on a columnar coil former with a same interval; two bundles of exciting coil wires with an interval of 180° are connected at an end of the columnar coil former, actually being a same group of exciting coil wire bundles; each pick-up coil part consists of two rows of pancake coils; each four pancake coils which are closely arranged in a square shape form one differential eddy current testing pick-up unit; a final output signal is a result of additions between signals of opposite pancake coils and subtractions between signals of adjacent pancake coils in each differential eddy current testing pick-up unit.