We report a combined photoelectron velocity map imaging spectroscopy and density functional theory investigation on the Au3H- anion. Transition between the anionic electronic ground state and the neutral electronic ground state is revealed. Vibrationally resolved spectra were recorded at two different photon energies, providing a wealth of spectroscopic information for the electronic ground state of the Au3H. Franck-Condon simulations of the ground-state transition are carried out to assist in the assignment of the vibrationally resolved spectra. The electron affinity and vertical detachment energy of Au3H are measured to be 2.548 +/- 0.001 and 2.570 +/- 0.001 eV, respectively. Three stretching vibrational modes are determined to be activated upon photodetachment, with the frequencies of 2100 +/- 100, 177 +/- 10, and 96 +/- 10 cm(-1).