The laser rapid forming (LRF) as an advanced solid freedom fabrication technology, has been developed rapidly in recent decade. By rapid prototyping with laser cladding, LRF realizes the direct net shaping of the components with irregular shapes and fine inner structures, and gives a short–route, low–cost and high–flexibility fabrication of aero components, aero–engine parts and biomedical implants. In the LRF, melting and solidification are happened in a dynamic non–equilibrium, high temperature gradient and rapid solidification manner, so that the microstructure of the laser rapid formed part is finer than that of ordinary cast or forge part and presents a characteristic of typical epitaxial growth. Therefore, to achieve the predict and control of the microstructure evolution is a key problem. Much efforts have been devoted to narrating the solidification and crystallization in melting pool, but little attention has been paid to stuy the microstructure of LRF part. In this paper, the evolution otemperture field and solidification of LRF part were concerned, the relationships between as–deposited microstructure and the local solidification conditions such as solidification velocity and temperaturgradient of moving melting pool were also investigeted. A coupled 2D transient finite element LRF epitaxial growth model was developed. The morphology evolution and first order dendrite arm space λ1 distribution in 2.8 mm high LRF 316L stainless steel wall were simulated. The results show that the microstructure of LRF 316L stainless steel wall is mainly columnar austenitic dendrites, and the λ₁ gradually becomes larger from the bottom about 6.5 μm to the top about 17 μm which is in good agrement with te experimntal. Further more, on the basis of the validated model, morphology volution and λ1 distribution in 40 mm high LRF 316L stainless steel wall are also predicted.