I have found a best solution for how to sort only current page in gridview in asp.net

Steps:-

1)Copy structure of the gridview in a datatable.
2)Then copy data of gridview in datatable.
3)Convert datatable to dataview (datatable doesn't have sort method).
4)Sort dataview by sort method.
5)Then again assign sorted data from datatable to gridview (not through datasource).

Go through the link to read more :-

Sorting only current page in a gridview in asp.net