【解决办法】可以通过ol.layer.Tile接口进行加载，具体示例代码如下：
var tmslayer = new ol.layer.Tile({
source: new ol.source.XYZ({
url: "http://localhost:8090/iserver/services/map-Population/tmsrest/1.0.0/PopulationDistribution/{z}/{x}/{-y}.png?transparent=true",
wrapX: true,
opaque:false
}),
projection: 'EPSG:3857'
});
map.addLayer(tmslayer);
