What is the correct grammar for following sentence i laid in sun?

The correct grammar depends on what you mean. Here are a few options:

* "I lay in the sun." This is the past tense of the verb "to lie" when it means to recline.

* "I laid down in the sun." This is the past tense of the verb "to lay" when it means to place something down.

The first option is more likely what you meant, as it describes a person relaxing in the sun.