A bit of a tricky question. I have depression, and I would say that kratom can help it in some ways, both by partially alleviating it and also by sometimes (for me, anyway), giving me a little more insight into it, if that makes sense.
However, if I'm quite seriously depressed and have kratom, it can actually exacerbate it. If I'm in a "good mood" (while still being depressed), it can boost my mood further and do as I said before; alleviate the depression while giving insight into it. But if I'm utterly depressed, it can make me even more depressed and make the depression pretty overwhelming. Since I've found this out, I am pretty selective when I have it, trying to make sure I'm not depressed enough already that it will make it worse.
I have found, though, that since I've been having kratom regularly (2-3 times a week), I've had less major depressed episodes and have understood my depression better. (I've also, possibly coincidentally, had less frequent schizophrenic episodes.)
The other problem you might find yourself in if you use it long-term for depression, of course, is addiction. Using it daily or several times daily, even if they're smaller doses, will increase your tolerance a good deal, you'll need more to achieve effects, and before long you'll be addicted. During withdrawals, depression can get a good deal worse.
All of this, of course, is just what I've personally found how it works on me, and it might be different for you.