Provided is a method of producing a composite, which is capable of preventing a silicone coating solution, which becomes a silicone resin layer that prevents an acidic gas separation layer from entering a porous support, from entering the porous support, preventing a porous film and an auxiliary support film from being peeled off, and suitably forming a dense silicone resin layer on the surface of the porous support. The method thereof includes a coating process of coating the surface of the porous film side of the porous support with the silicone coating solution which becomes a silicone resin layer according to a roll-to-roll system. In the coating process, the conveying speed of the porous support is in a range of 0.5 m/min to 200 m/min, the viscosity of the silicone coating solution is in a range of 100 cP to 1000000 cP, and the peel force between the porous film and the auxiliary support film is 10 mN/min or greater.