A novel spatial multilayer doubler is proposed in the paper. It is designed by tray approach in rectangular waveguide. The doubler consists of multilayer multiplier circuits, which are parallel each other. Comparing with traditional single layer doubler, the spatial multilayer doubler has higher 1dB compression point, so the output power can be increased when input power is increased. Both the input port and the output port of the doubler are rectangular waveguides. In order to achieve the transition from rectangular waveguide to planar circuit, the finline and ridge are used. Multilayer finlines act as divider, which couple power from input rectangular waveguide. Otherwise, multilayer ridges act as combiner, which combine the harmonic power to output rectangular waveguider. The passive circuits of the spatial multilayer doubler are modeled and analyzed with FDTD method. From the results, we can see that the passive circuits designed in the paper have very low insertion loss.