Steam turbine rotor is one of the key components of generator set. Fatigue cracks often occur at the anti T-root groove under the multiple effects of complex stress and high temperature, which leads to fracture accidents. The paper presents the total focusing ultrasonic phased detection method to solve the difficult problem of crack detection of anti T-root groove. In this paper, we deduced the transmitting sound field of total focusing phased array ultrasonic, and prepared the specialized specimens. Artificial defects are prefabricated by wire cutting method in the inverted circle (F1 area). Total focusing phased array ultrasonic is adopted to detect defects and compared with conventional ultrasound. The results show that total focusing phased array ultrasonic has high detection accuracy, strong adaptability and the good engineering application value.