There are a few of reasons why your
compost may smell, including:
The compost is too wet due to being
exposed to rain.
It contains too high a proportion of “green” materials such as grass clippings and food scraps.
It contains food scraps containing animal products such as meat, fish, skins or dairy products.
In the case of the first two the solution is similar – turn the compost and add some drier “brown” materials and mix thoroughly. If the compost is getting wet due to rain then make sure to cover it.
If you are putting meat or other materials of animal origin into the food scraps to be composted, these could be causing the smell. Collect only vegetative kitchen scraps for composting and consider using a Green Cone system or brown bin collection service for non-vegatative foods.