Abstract: Ultrasonic testing methods of small diameter bars with double crystal probe and immersion focusing probe were introduced. With 10 MHz immersion focusing probe and reference block, high sensitive ultrasonic testing with 0.5 mm equivalent for small bars about diameters 6mm and 8mm were realized, which solved the problem of testing bars after double crystal probe being damaged. The testing result showed that immersion ultrasonic method was very suitable for testing small mount and multi-specification bars and easy to control testing process.