Microcracks are defects that may occur in stainless steel sheets during use, and these cracks may affect the strength and stability of the material. The current detection methods are affected by interference sources such as sound, vibration, or electromagnetic waves in the surrounding environment when detecting these microcracks. The generated signals will be superimposed on the diffracted wave signal, causing the interference signal to mix with the diffracted wave signal, making it difficult to accurately extract the characteristics of the diffracted wave signal, thereby affecting the accuracy of crack angle detection. To this end, a laser ultrasonic diffraction wave detection technology for internal micro crack angles in stainless steel plates is proposed. Using laser ultrasound technology to detect the interior of stainless steel plates, generating ultrasound waves through laser excitation, and obtaining diffraction wave signals caused by microcracks. Perform anti-interference processing on diffracted wave signals to eliminate mixed interference noise in the diffracted wave signals. Conduct in-depth analysis on the diffraction wave signal processed by anti-interference, identify and extract features related to micro crack angle detection - diffraction wave propagation direction, diffraction wave energy distribution, amplitude, phase, and propagation time. Based on these features, a calculation formula for microcrack angle is constructed to achieve the calculation and detection of microcrack angle. The experimental results show that the maximum error between the microcrack Angle detection results obtained by this technique and the actual results is only 1.1°, and the shortest detection time is only 11.8 min, which fully confirms the superiority and high efficiency of the proposed technique.