Why this line showing up on both faces?

[kingston123]

Desired diagram: View attachment 2145

My diagram:View attachment 2146 (see the marking)

I applied edge chamfer on top edge (Length 1\length 2) as (10\35)

 

[MrCATIA]

I'm not sure why those lines show up. Maybe a software bug in CATIA?

Using Chamfer to taper the front and rear faces is an interesting technique. Chamfers are normally used to eliminate a sharp corner, like a fillet. They normally are short and don't extend the entire length of a face, like you've done. But there's nothing wrong with using a Chamfer for the tapered faces. Maybe it was confused with the slot in the middle?

You didn't show the tree diagram, so I have no idea what features were used to model what you have so far. And there are many ways to model a part like this.

But I suggest replacing the Chamfer with a Sketch and use a Pocket to cut-off the faces, like the picture below.

View attachment 2149

 

[kingston123]

Maybe it was confused with the slot in the middle?

YES. I applied edge chamfer before applying slot(pocket). Then I didn't get that line.