我没有好办法。
只能在最外面写个函数(如 function onInfoWindowBtnClicked)用来接收该Button的点击
而该button的html写成这样：
<input type="button" onClick="onInfoWindowBtnClicked()" />

自己编写一个WindowInfo
在其中添加你要添加的按钮，把这个按钮做成表单提交就可以了
function ShowClickMarker(marker) {
     GEvent.addListener
             (marker, "click",
                function (point) {
                    var inputForm = document.createElement("form");
                    if (marker.getTitle()) {
                        inputForm.id = 'marker_' + marker.getTitle();
                    }
                    else {
                        inputForm.id = 'marker_point';
                    }
                    inputForm.setAttribute("action", "#");
                    inputForm.onsubmit = function () {
                        Ext.getCmp('map_google').getMap().closeInfoWindow();
                        storeMarker(this.found.value);
                        return false;
                    };
                    var point = marker.getLatLng();
                    if (point) {
                        // Lat纬度;Lng经度
                        var n = point.lng();
                        var e = point.lat();


                        var Point = new GLatLng(e, n, true);
                        if (marker.getTitle()) {
                            inputForm.innerHTML =
               "<fieldset id='field1' style = 'width:300px'>"
             + "<lengend>" + marker.getTitle() + "信息：</legend>"
             + "
"
             + "<label for = 'left'>经度：</label>"
             + "<label for = 'left'>" + n + "</label>"
             + "
"
             + "<label for = 'left'>纬度：</label>"
             + "<label for = 'left'>" + e + "</label>"
             + "
"
             + "
"
             + "<a onclick='pathinfro()' href='#'>获取路线</a>"
             + "&nbsp;&nbsp;"
             + "<a href='#'>在附近搜索</a>"
             + "&nbsp;&nbsp;"
             + "<a onclick='SaveMap()' href='#'>保存到...</a>"
             + "&nbsp;&nbsp;"
             + "<a onclick='MarkerSearchBigger()' href='#'>在此处放大</a>"
             + "
"
             + "
"
             + "<div id='markerSerch'>"
             + "<input type ='text' id='found' style ='width:220px'/>"
             + "<input type ='submit' value = '搜&nbsp;&nbsp;&nbsp;&nbsp索' style ='float:right;'/>"


             + "</div>"
                            //+ '<br'
             + "</fieldset>";
                        }
                        else {
                            inputForm.innerHTML =
               '<fieldset id="field1" style ="width:300px">'
             + '<lengend>坐标点信息：</legend>'
             + '
'
             + '<label for = "left">经度：</label>'
             + '<label for = "left">' + n + '</label>'
             + '
'
             + '<label for = "left">纬度：</label>'
             + '<label for = "left">' + e + '</label>'
             + '
'
             + '
'
             + '<a onclick="pathinfro()" href="#">获取路线</a>'
             + '&nbsp;&nbsp;'
             + '<a href="#">在附近搜索</a>'
             + '&nbsp;&nbsp;'
             + '<a onclick="SaveMap()" href="#">保存到...</a>'
             + '&nbsp;&nbsp;'
             + '<a onclick="MarkerSearchBigger()" href="#">在此处放大</a>'
             + '
'
             + '
'
             + '<div id="markerSerch">'
             + '<input type ="text" id="found" style = "width:220px"/>'
             + '<input type ="submit" value = "搜&nbsp;&nbsp;&nbsp;&nbsp索" style ="float:right;"/>'
             + '</div>'
                            //+ '<br'
             + '</fieldset>';
                        }
                        Ext.getCmp('map_google').getMap().openInfoWindow(Point, inputForm);
                    }
                    else {
                        Ext.MessageBox.alert("提示", "未获取标记点信息！")
                    }
                });
代码可以这么写