Haniu, Dynamic is for displaying the whole map service and not a single layer. You can use type feature and get that one single layer if you specify your renderer in the XML. It all comes back to you using such an older ArcGIS Server.Here is an example.<layer type="feature" label="layer2" alpha="1.0" url="http://172.30.129.52/arcgis/rest/services/test_pl2b/MapServer"
visiblelayers="2" useamf="true" mode="onDemand" visible="true">
<uniquevaluerenderer field="type" fielddelimiter=",">
<uniquevalueinfo value="3" label="Campground">
<picturemarkersymbol url="assets/images/es.png" />
</uniquevalueinfo>
<uniquevalueinfo value="2" label="Contained Fire">
<picturemarkersymbol url="assets/images/fr.png" />
</uniquevalueinfo>
<uniquevalueinfo value="4" label="Damaged Home">
<picturemarkersymbol url="http://sampleserver3.arcgisonline.com/ArcGIS/rest/services/Fire/Sheep/FeatureServer/0/images/7D11DE72" />
</uniquevalueinfo>
<uniquevalueinfo value="0" label="Fire Department">
<picturemarkersymbol url="http://sampleserver3.arcgisonline.com/ArcGIS/rest/services/Fire/Sheep/FeatureServer/0/images/86A29AC1" />
</uniquevalueinfo>
<uniquevalueinfo value="6" label="Mountain">
<picturemarkersymbol url="http://sampleserver3.arcgisonline.com/ArcGIS/rest/services/Fire/Sheep/FeatureServer/0/images/41B1D33E" />
</uniquevalueinfo>
<uniquevalueinfo value="5" label="Ranger Station">
<picturemarkersymbol url="http://sampleserver3.arcgisonline.com/ArcGIS/rest/services/Fire/Sheep/FeatureServer/0/images/EEA508E3" />
</uniquevalueinfo>
<uniquevalueinfo value="1" label="Shelter">
<picturemarkersymbol url="http://sampleserver3.arcgisonline.com/ArcGIS/rest/services/Fire/Sheep/FeatureServer/0/images/B0F5149C" />
</uniquevalueinfo>
</uniquevaluerenderer>
</layer>
or<layer type="feature" label="layer2" alpha="1.0" url="http://172.30.129.52/arcgis/rest/services/test_pl2b/MapServer"
visiblelayers="2" useamf="true" mode="onDemand" visible="true">
<simplerenderer>
<simplemarkersymbol style="triangle" color="0xFF0000" alpha="1" size="40">
<outline width="2" color="0x0000FF" style="dashdot" />
</simplemarkersymbol>
</simplerenderer>
</layer>