The invention discloses a method and system applicable to a set top box and capable of adaptively outputting resolution. The method comprises the following steps of S1, connecting the set top box to atelevision and obtaining the highest resolution supported by the television; S2, connecting the set top box to a network, receiving a first receiving video signal, and analyzing the resolution of thefirst video signal; S3, using the set top box to convert the obtained first video signal into a second video signal according to the highest resolution supported by the television and the obtained resolution of the first video signal, and sending the second video signal to the television, wherein the resolution of the second video signal is not higher than the highest resolution supported by thetelevision. Therefore, the set top box automatically switches and outputs the resolution of the video signal according to the condition of the resolution supported by the television and the resolutionof the video signal by acquiring the resolution supported by the television, so that the best picture effect of the television is achieved.