A local refinement method of unstructured grid generated by bubble packing method(BPM)is proposed. In the present method

different size bubbles are added to the real and artificial vertices of the domain and bubble information of these vertices is transferred to the inner nodes of the domain by the Shepard interpolation method. Moreover

a method to control the population of bubbles is presented to add bubbles in large gap between bubbles and remove bubbles to eliminate overlapping so that the generation of skinny triangles is avoided and the grid quality is clearly improved. Furthermore

the improved BPM is applied to generate unstructured grid with local refinement near boundary for square domain to simulate the lid-driven flow in a square cavity with Re=1 000. The numerical result agrees well with the benchmark solution

indicating that the improved BPM is effective to the computation of fluid flow and heat transfer.