One-dimensional (1D) simulation tools, the computing speed of which is relatively fast, usually solve simple complexity problems. The solving process of 1D simulation is mostly based on one-dimensional dynamic equations and empirical laws and thus in some cases it cannot obtain a similar accuracy with the time-consuming three-dimensional (3D) simulation tools. The 1D-3D co-simulation, which combines the advantages of the two simulation tools while minimizes the disadvantages, is a method that integrates and runs the two simulation tools concurrently. The coupled simulation can offer a 3D analysis for which a detailed information is needed while offer system level information in the rest of the whole system where averaged results are sufficient. The approach not only minimizes the computational cost, but avoids demand for imposing accurate boundary conditions to the 3D simulation. But nowadays, a lot of paper only use the approach to obtain boundary condition from 1D environment, few study focus on the influence of 3D part on system. (e.g influence of intake or exhaust manifold on flow in cylinder in co-simulation).The objective of this study includes two aspects, one compares the difference between 1D and the 1D/3D coupling, the other studies the influence of the 4-1 and 4-2-1 exhaust manifold on in-cylinder residual fraction gas (RGF) based on the proposed 1D and 3D co-simulation approach.It describes a detailed analysis of the integrated 1D-3D simulation for two different exhaust manifold geometries on a turbocharged gasoline engine. The research results show that the induction process of the original 1D model and the co-simulation model were nearly equal, but the exhaust pressure of the coupled model was smoother than that of the original 1D model. The 4-1 exhaust manifold has a larger residual gas fraction due to the more severe pulse interference and the 4-2-1 exhaust manifold is able to mitigate this phenomenon by separating the runner 1/runner 4 with runner 2/runner 3. Furthermore, by added a spacer plate at exit port of 4-2-1 manifold, it can further reduce in-cylinder RGF and enable more uniformity among four cylinders. Therefore, the 4-2-1 exhaust manifold can be used to enhance the engine performance to achieve the concept of downsizing and down-speeding, and also it can be adopted to optimize the fuel efficiency by advancing the spark timing.