您可以有两个途径：

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        config.Routes.MapHttpRoute(
            name: "ApiById",
            routeTemplate: "api/{controller}/{id}",
            defaults: new { id = RouteParameter.Optional },
            constraints: new { id = @"^[0-9]+$" }
        );

        config.Routes.MapHttpRoute(
            name: "ApiByName",
            routeTemplate: "api/{controller}/{action}/{name}",
            defaults: null,
            constraints: new { name = @"^[a-z]+$" }
        );

        config.Routes.MapHttpRoute(
            name: "ApiByAction",
            routeTemplate: "api/{controller}/{action}",
            defaults: new { action = "Get" }
        );
    }
}