This paper describes necessity that quicken construct new south-north passage of west area，expounds and proves importance of Xi^an-Ankang railway in network，and suggests the- idea that influence of construction on transport capacity under circumstances of building second line nearby electrified railway in mountain area must be considered as well as conditions of in?crease second line and extand capacity during design new single track main railway should be considered too. Its viewpoint contributes valuable suggestions for making policy and designing.