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Additive manufacturing is believed to open up a new era in precise microfabrication, and the dynamic microstructure evolution during the process as well as the experiment-simulation correlated study is conducted on a prototype multi-principal-element alloys FeCrNi fabricated using selective laser melting (SLM). Experimental results reveal that columnar crystals grow across the cladding layers and the dense cellular structures develop in the filled crystal. At the micron scale, all constituent elements are evenly distributed, while at the near-atomic scale, Cr element is obviously segregated. Simulation results at the atomic scale illustrate that i) the solid-liquid interface during the grain growth changes from horizontal to arc due to the radial temperature gradient; ii) the precipitates, microscale voids, and stacking faults also form dynamically as a result of the thermal gradient, leading to the residual stress in the SLMed …