This paper constructs the game models of a supply chain under the dual-channel and online to offline (O2O) modes, and studies the pricing and mode selection in a supply chain under the influence of Showrooms effect. The results show that: no matter what the channel mode is, offline Showrooms service and Showrooms effect make the manufacturer and retailer increase the retail prices of both online and offline channels. The manufacturer decreases the wholesale price under the dual-channel mode, while it does not necessarily reduce the wholesale price under the O2O mode. The offline Showrooms service and Showrooms effect increase the demand of online and offline channels, which can increase the retailer's profit, thus the retailer would like to provide offline Showrooms service and accept the O2O mode. The manufacturer will also choose the O2O mode, when the Showrooms effect is negligible, which can improve the operation efficiency of a supply chain under most conditions. Therefore, when the Showrooms effect and the proportion of online channel demand meet certain conditions, the O2O mode is the consistent choice of the manufacturer and retailer, which realizes the successful transformation from dual-channel mode to the O2O mode.