You can pass three parameters like that.. :)
function CallWebService() {
$.ajax({
type: "POST",
url: "PageName.aspx/WebServiceMethodName",
data: "{'Param1':'" + Param1 + "','Param2':'" + Param2 + "','Param3':'" + Param3 + "'}",
contentType: "application/json",
dataType: "json",
success: function (msg) {
},
error: function (result) {
}
});
}