Numerical study on focal spot overlapping can provide important supports for the construction of an excimer laser angular multiplexing system. The simulation methods of focal spots overlapping are introduced first. And then simulations of 18 laser beams overlapping are performed based on single laser beam focal spot profiles and laser pointing stability. Profiles and parameters of overlapped laser focal spot on target surface are given. Finally, the relations between imaging quality and laser pointing stability are studied under the requirements of isentropic compression experiments. Many conclusions are drawn from the study. The uniformity of focal spot can be raised by overlapping. What′s more, better beam pointing stability is needed to keep the uniformity when the imaging quality is excellent. Otherwise, the outstanding imaging quality is wasteful. The beam pointing stability can just be within a certain range when imaging quality is common, for the uniformity cannot be improved much by better laser pointing stability.