An high-pressure reactor acid adding system for laterite nickel ore hydrometallurgy includes: an acid liquor supply tank, an acid adding pipe, an acid adding pump, a pressure stabilizer, and a high-pressure reaction kettle, where one end of the acid adding pipe is communicated with the high-pressure reaction kettle, the other end thereof is communicated with the acid liquor supply tank, and the acid adding pump is disposed on the acid adding pipe and is configured to pressurize and pump acid liquor in the acid liquor supply tank to the high-pressure reaction kettle through the acid adding pipe; and the pressure stabilizer is disposed on the acid adding pipe and is configured to dynamically accommodate or discharge the acid liquor, to reduce pressure fluctuation in the acid adding pipe. Compared with the prior art, according to this disclosure, the pressure stabilizer is disposed on the acid adding pipe, the pressure stabilizer can accommodate a part of the acid liquor when pressure in the acid adding pipe is too high, to reduce the pressure of the acid adding pipe, or discharge a part of the acid liquor when pressure in the acid adding pipe is too low, to increase the pressure of the acid adding pipe, thereby reducing pressure fluctuation in the acid adding pipe, maintaining pressure of the acid liquor in the acid adding pipe within an appropriate range, and helping improve an acid leaching effect in the high-pressure reaction kettle.