Abstract: The detection sensitivity of the water immersion line focusing probe for controlled jet ultrasonic testing of steel plate production line is affected by many factors. In order to explore the degree of influence of various influencing factors on the probe, different experimental conditions were designed for each factor. The results show that the deflection angle of the probe and bubbles are the factors that have the greatest influence on the sensitivity of the probe, and the turbidity of water within a certain range does not have obvious influence on the detection sensitivity. The research results of influencing factors are of great significance to the formulation of related testing techniques and standards.