Abstract: In order to research on the effects of different parameters on microstructures of Ni-based superalloy formed by plasma arc additive manufacturing,and Inconel 718 superalloy samples were fabricated by using the heat resource of pulse plasma arc.Simple Variable Method（SVM）was used to study the influence of peak current,pulse frequency and welding speed on microstructures of the as-fabricated samples.Various material characterization methods such as optical microscope,scanning electron microscope,and energy spectrum analysis were carried to study the effects of different parameters on the microstructure morphology,grain size,and component distribution in consideration of temperature gradient and crystallization rate.Results show that microstructures of the as-fabricated samples change from fine columnar dendrites to coarse cellular dendrites with the increase of peak current,and meanwhile the number of Laves phases increases.On the contrary,the increase of welding speed contributes to fine grains.Microstructure interestingly become coarse due to unsuitable pulse frequency.