If you like to play around with Photoshop's Layer Styles, sooner or later you'll run into this problem. If you try to apply a mask to a layer that uses Layer Styles, you won't get what you expect, unless you expect your Layer Styles to be all messed up.
Here's a simple text effect I created using Layer Styles:
I'm going to apply a black-to-white gradient to the text's layer mask so that the text will appear to gradually fade away as you get closer to the bottom. We can see the gradient I applied in the layer mask thumbnail in the Layers palette:
We should see the text gradually fading out from top to bottom, but instead, we get this:
Not exactly what I was looking for. The reason is that by default, masks don't have the same effect on Layer Styles as they do on the layers themselves, but we can change that. All you need to do is click on the New Adjustment Layer icon at the bottom of the Layers palette, just as if you were going to apply a Layer Style, but rather than choosing "Drop Shadow" or "Stroke", choose the option at the very top, Blending Options. This will bring up the Layer Style dialog box set to the Blending Options.
If you look in the Advanced Blending options in the middle, you'll see an option called Layer Mask Hides Effects. Click inside the checkbox to the left of it to select it:
Now your Layer Styles will behave as you expected.
Here's my same text effect with the mask applied after checking that option:
I don't know why that option isn't turned on by default, but it isn't, so make sure you enable it and your Layer Styles and masks will work together as you'd expect them to in Photoshop.
source : www.photoshopessentials.com