As a free forming additive manufacturing technology for high performance metal parts, laser deposition manufacturing has a broad application prospect in aerospace and other fields. The solidification behavior and microstructure of molten pool determine the mechanical properties of the deposited parts. A multi-scale Cellular Automaton (CA)- Finite Element (FE) model is developed to simulate the microstructure evolution with different process parameters during the Direct Laser Deposition (DLD) process. Temperature data and solidification parameters under different process parameters are obtained by finite element method, which establish connections between macroscopic temperature field and microstructure simulation. In addition, the effects of different process parameters on dendrite morphology, element segregation and grain structure are investigated. The primary dendrite arm spacing (PDAS), Nb element precipitation and grain size all increase with the increase of laser power, which are caused by the decrease of cooling rate. Moreover, the trend of the simulated results of microstructure under various process parameters are consistent with the experimental results.