why every time i bake a cake in microwave it burns in middle and rest of the cake is uncooked?

Microwave cooks from the inside out so that's why it cooked in the middle. You likely cooked using full power and for most microwaves you should use the MW at 70-80% power. You may have to experiment a bit to know which is best. Most recipes do say cook at 100%, but some MWs are too powerful. For yours, it is obviously cooking too fast in the middle so next time, try using the microwave at 70% power.

And for those who don't know, YES, you can bake successfully in the microwave.

Here's a link with some good tips:

http://chefinyou.com/2010/08/baking-in-microwave-m...

The microwave isn't the way to cook a cake. Use the oven.

Use an oven. You can't bake anything in a microwave.