In vivo, folding of many proteins occurs during their synthesis in the ribosome and continues after they have escaped from the ribosomal exit tunnel. In this research, the authors investigate the confinement effects of the ribosome on the cotranslational folding of three proteins, of PDB codes lPGA, lCRN and 2RJX, by using a coarse-grained model and molecular dynamics simulation. The exit tunnel is modeled as a hollow cylinder attached to a flat wall, whereas a Go-like model is adopted for the proteins. The results show that the exit tunnel has a strong effect on the folding mechanism by setting an order by which the secondary and tertiary structures are formed. For protein lPGA, the folding follows two different folding routes. The presence of the tunnel also improves the foldability of protein.