Female solder have no dress

Which race did you use? Perhaps that race has no dresses. If its a custom race you'll need to define all their dresses.

Who fights in a dress?

On a similar note... no one making a kilt mode? lol...

I think that a couple races (Krax and Ironeers IIRC) didn't have any bottoms for women (outside the actual armour ones) in the unit designer (for soldiers, not sovereigns).  Unless I completely missed it or such.  Though the Ironeers at least did have dresses among the tops.  

Race is Wraith. My daughter and the lady of the quest wear the dress,but in the design screen of solders ,I can't find them. 

I find the reason.Maybe in Wraith ,dress is the marker of noble.

I make a new faction of man, the solder of them have dress,now.

Some dresses seem restricted.

Looking in \\English\CoreRobesDresses.xml

It's the usual mess of Stardocks XML though, there is an overabundance of some tags, and some are limited to Empire and some are Limited to Kingdom. Some further racial specific.

You need to look at

    <SupportedUnitModelType>KingdomFemale</SupportedUnitModelType>
    <SupportedUnitModelType>EmpireFemale</SupportedUnitModelType>

Look here.