As the use of liquid lithium (Li) as the plasma facing material in a fusion device becomes widespread, more and more research work has been dedicated to the numerical simulations of Li flow based on the Navier-Stokes equations. However, the slip condition of Li on a solid surface hasn’t been fully understood. The most common and simplest boundary condition, which is no-slip, is just one of the allowable conditions ranging from pure slip to multi-layer locking. In this work, molecular dynamics simulations of the Couette flow were performed to investigate the slip properties of liquid Li on tungsten (W) surfaces. The atomic structures near the surfaces were inspected. The influence of temperature, lattice orientation and biaxial strain of wall surfaces, as well as the surface roughness, were discussed. It was found that the slip length is always negative suggesting that the wall always retards the movement of liquid Li. Among all the factors, surface roughness has the most significant effects on the slippage. Two sectional linear relationships between the slip length and the height of the roughness elements were discovered. As the height of roughness elements reaches a critical point, micro vortexes begin to form and change the slope of the linear relationship.