The nondestructive characterization of pitting corrosion of 304 austenitic stainless sheets of steel is realized by nonlinear ultrasonic surface wave detection technique. The solid solution 304 austenitic stainless sheets of steel are soaked in the FeCl3 of 6.0%, 10.0% and 14.0% for 6, 12, and 18 h respectively. The surface morphology of the samples soaked is observed by OLS4000 laser confocal microscope, and the three-dimensional morphology and size of the steady-state pitting holes are measured. The nonlinear coefficient of the ultrasonic surface wave is measured by RAM5000. The normalized nonlinear coefficient is analyzed based on the morphology and dimensional change of the pits. The results show that the normalized nonlinear coefficient rises gradually with the increasing ultrasonic surface wave spreading distance. When the surface wave spreading distance is constant, the normalized nonlinear coefficient is significantly increased with the increase of soaking time and the mass fraction of the solution. It is concluded that the stress-strain nonlinear effect resulted from the interaction of ultrasonic wave and discontinuous interface around pits tends to be remarkable with the increasingly serious pitting damage.