Graduation ceremony

I will go to USA in May, to attend my daughter's graduation ceremony.

The months of the year should use capital letters as these are proper nouns, you might also consider using "I will be going to the USA" as it makes the statement more freindly, rather than as is appears more like a fact..   

Graduation ceremony

I will go to USA in may,to attend my daughter's graduation ceremony.

Try this instead: I will go to the USA in May to attend my daughter's graduation ceremony.