Channels are one of the most important parts of systems related with micro and nano devices that are used for fluid transfer in different situations including heat transfer, material traort and fuel supply. With respect to the dimensions of these equipments, they have a characteristic length in micro and nano scales. The recognition of fluid behavior in nano-channels regarding their wide applications, have a great portion in attributes prediction of this kind of systems. Therefore, an appropriate method should be used for analysis of these channels. Due to the hardware limitations in analysis of flow behavior in micro and nano scales, numerical simulations are suitable methods for simulating of these types of systems, as complementary of experimental methods. In addition, with respect to measurement sensibility in these devices, one simulation method should be considered that has high accuracy. So, in this study, molecular dynamic simulation which is an accurate simulation method in molecular systems is used. This method is based on the second law of Newton that is used for predicting particle interaction by statistical mechanic. One of the justify; MARGIN: 0cm 0cm 0pt; unicode-bidi: embed; DIRECTION: ltr; tab-stops: 175.95pt" In this thesis by using molecular dynamic simulation method, the effect of different geometries of surface roughness on flow characteristics of liquid Argon in a nano-channel has been studied. Different types of roughness geometries that have been investigated in this study are rectangular, trapezoidal, triangular and cylindrical. Also roughness geometry with checker elements including spherical and cubical shape is used. The effects of various parameters such as roughness height, space between roughness elements and relation of energy depth have been studied. Results obtained, show that roughness height and space between roughness elements have a significant effect on the flow characteristic. By increasing the roughness height, the slip velocity and the maximum velocity will decrease while the density fluctuation will increase. On the other hand, by decreasing the space between the roughness elements the flow velocity will decrease. Also, results show that values of density fluctuation is independent of roughness geometry. In the recent years, open source softwares widely used for various scientific applications such as molecular science and molecular simulation. LAMMPS (Atomic Molecular Massively Parallel Simulator Large-scale) is one of the more applicable and famous of them. In the 5 recent years, many of researchers used it for their subjects and develope it for various subject of molecular science simulation. It has beenused in our case too. Keywords :Molecular dynamics simulation, poiseuille flow, Roughness geometry, N ano-Channels