A three-dimensional, nineteen-velocity (D3Q19) Lattice BoltzmannMethod (LBM) modelwas developed to simulate the fluid flow of a laminar square jet in cross flows based on the single relaxation time algorithm. The code was validated by the mathematic solution of the Poiseuille flow in a square channel, and was further validated with a previouswell studied empirical correlation for the central trajectory of a jet in cross flows. The developed LBMmodel was found to be able to capture the dominant vortex, i.e. the Counter-rotating Vortex Pair (CVP) and the upright wake vortex. Results show that the incoming fluid in the cross flow channel was entrained into the leeside of the jet fluid, which contributes to the blending of the jet. That the spread width of the transverse jet decreaseswith the velocity ratio. A layer-organized entrainment pattern was found indicating that the incoming fluid at the lower position is firstly entrained into the leeside of the jet, and followed by the incoming fluid at the upper position. (C) 2016 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.