This is working. I have resolve my issue by this solution. Thanks. Danail Vasilev
I have use something like below.
function OnClientSeriesHovered(sender, eventArgs) {
var chartObject = $find("<%=RadHtmlChart1.ClientID %>")._chartObject;
chartObject._tooltip.chartPadding.top = 15;
chartObject._tooltip.chartPadding.left = 15;
}
