Or "Catholic Fiction," for that matter. I think it was CS Lewis who said that speaking of "Christian fiction" is like speaking of "Christian gardening" and just as unhelpful. Is a "Christan garden" one in which you'd find a statue of St. Francis or stations of the cross along the path? Where all the flowers have religious names like "jack-in-the-pulpit"? Where the gardener sings "In the Garden" while at work in the hope that neighbors will hear her and convert?
This is silly, of course. One might argue, nontheless, that a gardener who is consciously Christian will bring to the work an appreciation for nature, a gratitude for the created order, perhaps even a sense of stewardship ala Genesis 2:15. In a similar way, an artist with Christian sensibilities will bring to the work a baptized imagination (as Lewis called it) with an eye for what is true, good, and beautiful, as per Paul's injunction in Philippians 4:8--
"Whatever things are true, whatever things are just, whatever things are pure, whatever things are lovely, whatever things are of good report, if there is any virtue and if there is anything praiseworthy - meditate on these things."
Not that everything be sanitized, sentimental, superficial or syrupy, obsessed with the sensational portrayal of demons and End-Times scenarios and covertly committed to winning souls. This is the stereotype and it is, unhappily, well-deserved.
Instead, I think a writer who happens to be Christian naturally produces work that is informed by an honest and full anthropology built on a Biblical premise - a view of humans as imbued with dignity, being made in the image and likeness of God, and yet fallen. Even so, renewal is possible, though not always achieved, given free will.
Christian writers are mindful of the fact that the Bible itself is composed primarily of narrative and poetry. It is telling, is it not, that when God wanted to communicate with humans, He used stories and songs. When Jesus Himself wished to make a point, he often told a short story.
Others have spoken with depth and clarity about this subject: CS Lewis, JRR Tolkien, GK Chesterton, Auden, Madeleine L'Engle (in her book "Walking on Water"), Flannery O'Conner ("Mystery and Manners") and even John Gardner's book is useful in this regard ("On Moral Fiction").
And there is an intelligent and insightful discussion on this topic in this discussion area, where I've posted a few comments as well.