Abstract: A fusion of acoustic images obtained by scanning probe acoustic microscope (SPAM) was studied under different acoustic frequencies. Firstly, SPAM was used to detect the breast cancer cells, MDA-MB-231 cells, and the acoustic frequency was changed within the range of 3~3 000 kHz to explore its effect on the acoustic imaging of breast cancer cells. Then the acoustic images of breast cancer cells were fused with an image fusion method, combining multi-scale transformation and sparse representation. The results show that, there exists a significant difference in the acoustic images obtained from the same sample under different acoustic frequencies. Moreover, useful information of different acoustic images can be synthesized by image fusion, which is more conducive to direct observation by human eyes or subsequent processing by computer.