countif from multiple sheet (In google sheets)

I want to to count value across multiple sheet in google excel sheets .Can anybody please help me out for this .

I don't believe Google Sheets can work across multiple worksheets. You'd either need something like

=COUNTIF(Sheet1!A3:Z1000,x)+COUNTIF(Sheet2!A3:Z1000,x)+...+COUNTIF(Sheet99!A3:Z1000,x)

or you'd need to consolidate your data into a single worksheet and use condition sums on that consolidated range.