Thank you all, for your answers. But i solved this with editing combo box control template.
Combo Box Control Template consist of three parts.
One is ToggleButton, second ComboBoxTextBox and ComboBox itself. To add an icon to combobox you must edit the ToggleButton control template.
At Microsoft site you can find the combo box control template.
http://msdn.microsoft.com/en-us/library/ms752094%28v=vs.85%29.aspx[
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Here is an toggle button example with an icon.
<controltemplate x:key="ComboBoxToggleButtonIcon" targettype="ToggleButton" xmlns:x="#unknown">
<grid>
<grid.columndefinitions>
<columndefinition width="0" />
<columndefinition />
</grid.columndefinitions>
<border x:name="Border" grid.columnspan="2" cornerradius="2" borderthickness="1">
<border.background>
<imagebrush imagesource="/images/icon.png" stretch="None" />
</border.background>
</border>
<border grid.column="0" cornerradius="0,0,0,0" margin="0" background="Transparent" borderbrush="Transparent" borderthickness="0,0,0,0" />
<path x:name="Arrow" grid.column="1" fill="#444" horizontalalignment="Right" verticalalignment="Center" margin="0,0,10,0" data="M 0 0 L 4 4 L 8 0 Z" />
</grid>
<controltemplate.triggers>
<trigger property="ToggleButton.IsMouseOver" value="true">
...
</trigger>
<trigger property="ToggleButton.IsChecked" value="true">
...
</trigger>
<trigger property="IsEnabled" value="False">
...
</trigger>
</controltemplate.triggers>
</controltemplate>
You can use this toggle button in your combo box control template with name.