Abstract: Objective In order to understand material defects and hardening of 304 austenitic stainless steel manufactured by laser metal deposition, it provides a reference for the subsequent engineering application of metal materials manufactured by this technology. Methods In this paper, material defects of 304 austenitic stainless steel manufactured by laser metal deposition and hardening phenomenon under monotonic/cyclic loading were studied. Results The results showed that the surface of laser metal deposition formed material was very rough and had obvious stacking traces. There were some defects such as holes, oxide inclusions and unmelted particles in the forming materials. Under the monotone loading, the formed material showed strain hardening, and strain hardening index was 0.4, which was lower than that of the material manufactured by traditional forging process. Under the cyclic alternating load controlled by strain, the formed material produced cyclic hardening at the initial stage of the test, while under the cyclic alternating load controlled by lower stress, the formed material produced cyclic softening at the initial stage of the test, and the formed material produced cyclic hardening with the increase of cyclic loading times. Conclusion Due to the unique forming process, material defects of 304 austenitic stainless steel manufactured by laser metal deposition were inevitable, and hardening phenomenon occurred under monotone load, strain-controlled cyclic alternating load and low stress controlled cyclic alternating load.