Disclosed is a high-pressure reactor comprising a reactor with one end as a feed inlet and the other end as a discharge outlet. Inside the reactor, a plurality of partition plates are arranged along the material flow direction, dividing the interior cavity of the reactor into multiple compartments, each compartment is equipped with a mixing device; the upper parts of any two adjacent compartments are connected; on the compartment for feeding material, an ore pulp inlet, a steam inlet, and an acid inlet are sequentially arranged circumferentially along the stirring direction with the mixing device in the compartment as the axis. In this disclosure, after the ore pulp enters the reactor vessel, under the stirring action of the mixing device, the ore pulp first comes into contact with steam to continue heating up, and then it contacts the acid to react with it. The reaction with the acid is exothermic, and the heat generated by the reaction is utilized to heat the newly incoming ore pulp.