File upload Jquery WebApi

Instead of submit button can you try with normal button –

<form enctype="multipart/form-data">
    <label>
        Using JQuery
    </label>
    <input name="file" type="file" id="me" />
    <input type="button" id="Upload" value="Upload" />
</form>

<script src="https://stackoverflow.com/questions/21497944/~/Scripts/jquery-1.10.2.min.js"></script>
<script type="text/javascript">
    $(function () {
        $('#Upload').click(function () {
            var formData = new FormData();
            var opmlFile = $('#me')[0];
            formData.append("opmlFile", opmlFile.files[0]);

            $.ajax({
                url: 'http://localhost:23133/api/file',
                type: 'POST',
                data: formData,
                cache: false,
                contentType: false,
                processData: false
            });
        });
    });
</script>

Controller Action –

    public HttpResponseMessage Post()
    {
        HttpResponseMessage result = null;
        var httpRequest = HttpContext.Current.Request;

        // Check if files are available
        if (httpRequest.Files.Count > 0)
        {
            var files = new List<string>();

            // interate the files and save on the server
            foreach (string file in httpRequest.Files)
            {
                var postedFile = httpRequest.Files[file];
                var filePath = HttpContext.Current.Server.MapPath("~/" + postedFile.FileName);
                postedFile.SaveAs(filePath);

                files.Add(filePath);
            }

            // return result
            result = Request.CreateResponse(HttpStatusCode.Created, files);
        }
        else
        {
            // return BadRequest (no file(s) available)
            result = Request.CreateResponse(HttpStatusCode.BadRequest);
        }

        return result;
    }

Output –