百度地图javascript api 中如何画圆弧

你可以用添加/删除覆盖物这个API试试
// 百度地图API功能
var map = new BMap.Map("allmap");
var point = new BMap.Point(116.404, 39.915);
map.centerAndZoom(point, 15);

var marker = new BMap.Marker(new BMap.Point(116.404, 39.915)); // 创建点
var polyline = new BMap.Polyline([
new BMap.Point(116.399, 39.910),
new BMap.Point(116.405, 39.920),
new BMap.Point(116.425, 39.900)
], {strokeColor:"blue", strokeWeight:2, strokeOpacity:0.5}); //创建折线

var circle = new BMap.Circle(point,500,{strokeColor:"blue", strokeWeight:2, strokeOpacity:0.5}); //创建圆

var polygon = new BMap.Polygon([
new BMap.Point(116.387112,39.920977),
new BMap.Point(116.385243,39.913063),
new BMap.Point(116.394226,39.917988),
new BMap.Point(116.401772,39.921364),
new BMap.Point(116.41248,39.927893)
], {strokeColor:"blue", strokeWeight:2, strokeOpacity:0.5}); //创建多边形

var pStart = new BMap.Point(116.392214,39.918985);
var pEnd = new BMap.Point(116.41478,39.911901);
var rectangle = new BMap.Polygon([
new BMap.Point(pStart.lng,pStart.lat),
new BMap.Point(pEnd.lng,pStart.lat),
new BMap.Point(pEnd.lng,pEnd.lat),
new BMap.Point(pStart.lng,pEnd.lat)
], {strokeColor:"blue", strokeWeight:2, strokeOpacity:0.5}); //创建矩形

//添加覆盖物
function add_overlay(){
map.addOverlay(marker); //增加点
map.addOverlay(polyline); //增加折线
map.addOverlay(circle); //增加圆
map.addOverlay(polygon); //增加多边形
map.addOverlay(rectangle); //增加矩形
}
//清除覆盖物
function remove_overlay(){
map.clearOverlays();
}
不过这需要三角函数，关于三角函数可以去看一下《揭秘javascript的三角函数》这篇文章，那里面对三角函数讲得很清楚了。
参考资料：

《揭秘javascript的三角函数》来自：http://www.tulingit.cn/?p=320