$('#myButton').click(function() {
    $('#Grid input[type=checkbox]:lt(5)').attr('checked','checked');
});

如果网格中还有其他复选框，则可能存在问题.这是我***的办法，而又看不到您的HTML.

If you have other checkboxes in the grid, there may be in issue. This is the best I can do without seeing your HTML.