Abstract: To better understand the distribution of laser light in biological tissues，this paper adopted the Monte Carlo model with laser wavelengths of 532，800，and 1 064 nm，respectively，for simulation study of photoacoustic imaging of human tissues. Under the conditions of different laser wavelengths and different incident spot sizes，the distribution of the penetration light intensity of human tissues and the main factors affecting the spatial distribution of laser energy was studied，and the relationship between the penetration depth of the laser and the light intensity in the tissue was obtained. The effect of laser on the initial acoustic pressure of biological tissues was studied，and the best experimental protocol was given under three wavelengths of the laser. The experimental results showed that the penetration depth had an important effect on the size of the laser energy distribution region in the laser incidence direction. The laser with a wavelength of 1 064 nm was more suitable for deep tissue imaging due to its higher maximum allowable exposure.

Key words: biomedical, photoacoustic imaging, wavelength, fluence