The interaction between the inner, surface and near- surface defects of laser solid forming TC4 alloy and ultrasonic are studied. The results show that under the same testing conditions, reflection amplitude value increases with the increasing of long lateral hole diameter for the long lateral hole defects with the same depth and different diameters; and the reflection amplitude value decreases with the increasing of the depth of long lateral hole for the long lateral hole defects with the same diameter and different depths; holes within 0.6 mm diameter can be found in laser solid forming TC4 alloy using 5PФ8 straight longitudinal wave probe. The ability of SAW to found defects less than 4mm from the surface in the depth direction is less than 4 mm and the hole defect is harder to find than the groove.