我刚想通了.有一个PackageManager.getDefaultActivityIcon()方法返回一个Drawable.如果Drawable的Bitmap与应用程序图标Drawable的Bitmap匹配,则它是默认图标.

PackageManager pm = context.getPackageManager();

Drawable icon = pm.getApplicationIcon(apk.package_name);

Drawable default_icon = pm.getDefaultActivityIcon();

if (icon instanceof BitmapDrawable && default_icon instanceof BitmapDrawable) {

BitmapDrawable icon_bd = (BitmapDrawable)icon;

Bitmap icon_b = icon_bd.getBitmap();

BitmapDrawable default_bd = (BitmapDrawable)pm.getDefaultActivityIcon();

Bitmap default_b = default_bd.getBitmap();

if (icon_b == default_b) {

// It's the default icon

}

}