The utility model discloses a small-sized reaction injection molding device. The small-sized reaction injection molding device comprises two material tanks for injecting quantitative corresponding materials and a mixing head for mixing materials by utilizing high-pressure collision, wherein each material tank is communicated with the mixing head through a corresponding discharging pipe; the material tank is connected with a feeding pipe and is selectively connected with a gas inlet/outlet pipe of a high-pressure insert gas source or a vacuum pump; corresponding switching valves are respectively arranged in series on the discharging pipes, the feeding pipes and the gas inlet/outlet pipes. According to the small-sized reaction injection molding device provided by the utility model, the switching valves are arranged on the discharging pipes, and the material tanks can accumulate pressure by closing the switching valves when the high-pressure insert gas source fills insert gas into the material tanks, so that high pressure which is required in a reaction injection molding process is guaranteed. The small-sized reaction injection molding device is simple in structure, simple and convenient to operate, small in size, low in cost, applicable to formula and condition test research and also applicable to teaching demonstration experiments.