A three-dimensional(3D)hydrodynamic model was developed based on FLOW-3D. The influences of the lateral spacing and relative installation elevation of the turbines and incoming velocity on the hydrodynamics around two parallel-arranged horizontal-axis tidal stream turbines were investigated. Numerical results show that an increase of the lateral spacing between two turbines leads to a decrease of the maximum fluid force acting on the turbines in the flow direction, with a maximum decrease of 6. 62%, and a decrease of the maximum velocity in the accelerating region of the wake field, with a maximum decrease of 1. 21%. The changes of relative installation elevation of turbines and incoming velocity have significant impacts on the rotating speed of turbines, maximum fluid force acting on turbines, and the velocity distribution within the wake field.