A hole-jetting type mixer-reactor, comprises the following parts: a first feeding port, a second feeding port, an outer casing, an inner casing, jet holes and a mixing reaction zone. The inner casing is inside the outer casing, and the lower portion of the outer casing forms a buffer chamber with the inner casing. The first feeding port connects with the inner casing to constitute one flow channel, and the second feeding port connects with the buffer chamber to form the other flow channel. The jet holes are on the wall of the inner casing situated at lower portion of the buffer chamber. The mixing reaction zone is inside the inner casing below the jet holes. The cross section of the inner casing is rectangular or rectangle-like. The mixer-reactor can achieve a fast mixing of two reactant streams which reacts with instantaneous, complicated parallel or consecutive competing reactions. The time scale of the mixing process is several milliseconds.