population number keep rising,aprroval number keep reducing. how to do i stop it?

Your population will keep on increasing until it reaches the maximum for that planet (usually appears right beside the current population). The more people on a planet the less happy they'll get. Duh, who wants to live with other people on the same planet?

You can build buildings that have an approval bonus (yellow smiling face). But it won't help if there are way too many people on the planet (like 20b).

oohh okl tnx

Also, keeping your tax rate low will help keep morale up.  And if you find any morale resources (the yellow ones), build constructors and build on them to get added morale improvements.