Abstract: In order to obtain the uniform inverted pyramid micro-structures on the surface of multi-crystalline silicon, this paper presents a new way of using two orthogonal ultrasonic standing waves exerted dimensionally to assist wet chemical erosion and improve the performance of light trapping. A 2D geometrical mode of grid-like arrangements is established firstly after some comparison. Then the theory of particles aggregation motion formatting the grid-like model under the field of ultrasonic standing waves is studied and verified with simulation tool. Experiments are carried out to test the effects of particles controlled motion. The multi-crystalline silicon erosion results illustrate that the idea of application of ultrasonic standing waves on grid micromachining is feasible and excellent.