A mechanics experiment system for a perforated string in underground perforating blasting of an oil-gas well. The system includes an experiment water pool, a perforated string arranged in the experiment water pool, a signal amplifier, an A/D converter and a computer. The signal amplifier, the A/D converter and the computer are arranged outside the experiment water pool and are sequentially electrically connected; the perforated string includes an oil pipe, a packing tube, a sleeve, an acceleration testing short joint A, a damper, an acceleration testing short joint B and a perforating gun which are sequentially connected from top to bottom.