The present invention provides a media stream playing method and a set-top box. In the present invention, in a process that a guidance unit of a set-top box initializes a platform system, the guidance unit obtains a channel identifier of a channel to be played and obtains, by using the channel identifier, a media stream that corresponds to the channel identifier, so that the guidance unit can send the media stream to a playing unit of the set-top box for playing. Because the technical solution is independent of the platform system of the set-top box, a problem in the prior art that, the set-top box cannot perform a television play service in an initialization process of the set-top box and the set-top box can perform the television play service by using the platform system only after the initialization of the set-top box is completed, can be avoided.