Improper setting, check the phone Settings: open 'wlan', press the menu to select 'Advanced', look for 'Maintain wifi connection in sleep state', set it to 'always'. It is also possible that the phone's installation package itself is defective. First restore the appearance Settings, if not, a brush should be able to solve.
Housekeeping software causes: This type of housekeeping software is installed and the power saving mode is set. As long as the standby state automatically disconnect wifi cancel. If you do not know how to cancel the butler software, the easiest way is to \"disable\" the mobile phone butler software in the application first. When used, line \"Enable\" again.