Abstract: Numerical photoacoustic models were constructed to study photoacoustic signals from metal nano-particles under pulse excitation in infrared based on the finite element algorithm.Gold nanotubes with gel shells were taken as the example to investigate the influence of gel shells on the acoustic signals.The gel shell can promote the signal greatly and the maximum one is about 6 times of that from naked nanotubes.It is also found that the strongest acoustic signal can be got only if the structural parameters of the nanotubes are tuned to make the surface plasmon resonance match with the incident light.This work can serve as a reference for the infrared photoacoustic contrast agents.