Since DNA methylation alters the chromatin state and regulates gene expression, elucidating the regulatory mechanisms of DNA methylation in response to environmental changes in the cell is crucial and urgent in understanding and regulating DNA methylation. G-quadruplex (G4) regulates transcription, translation and replication. Although it has recently been suggested that G4 regulates methylation, the detailed regulatory mechanism remains unclear. Here, we systematically analysed the effect of G4 formation on DNA methylation using G4s with various stabilities and topologies. The methylation efficiency decreased as the stability of G4 increased. Moreover, the degree of methylation suppression can be also controlled by G4 topology. Furthermore, our results showed the possibility of regulating methylation by modulating G4 stability and topology.