The present invention discloses a power saving method of a portable Internet device, the portable Internet device and its instant messaging system. If a screen of the portable Internet device is in non-view state, for example, both backlight module and LCD panel are turned off, it means that a user is not viewing the screen, and thus the message update frequency of the instant messaging program is lowered to prevent unnecessary transmission and receiving of wireless signals, so as to reduce power comsumption of the portable Internet device.