所以问题似乎是outerPadding.但是将outerPadding设置为零并没有帮助.但是,当我使用rangeBands时,问题就消失了,并且杆正确定位在轴的正下方.但是我会得到这些令人讨厌的抗锯齿效果,所以这不是一个真正的选择.这是我的代码：

var margin = {top: 40,right: 40,bottom: 20,left: 20},width = 900 - margin.left - margin.right,height = x - margin.top - margin.bottom;

    var x = d3.scale.linear().range([0,width]);

    var y = d3.scale.ordinal().rangeRoundBands([0,height],.15,0);

    var xAxis = d3.svg.axis()
            .scale(x)
            .orient("top");

    var xAxis2 = d3.svg.axis()
            .scale(x)
            .orient("bottom");

    var xAxis3 = d3.svg.axis()
            .scale(x)
            .orient("bottom")
            .tickSize(-height,0)
            .tickFormat("");

    var svg = d3.select("#plotContainer").append("svg")
            .attr("width",width + margin.left + margin.right)
            .attr("height",height + margin.top + margin.bottom)
            .append("g")
            .attr("transform","translate(" + margin.left + "," + margin.top + ")");


    x.domain(d3.extent(data,function(d) {
        return d.size;
    })).nice();
    y.domain(data.map(function(d) {
        return d.name;
    }));

    svg.append("g")
            .attr("class","x axis")
            .call(xAxis);
    svg.append("g")
            .attr("class","x axis")
            .attr("transform","translate(0," + height + ")")
            .call(xAxis2);
    svg.append("g")
            .attr("class","grid")
            .attr("transform"," + height + ")")
            .call(xAxis3);

    svg.selectAll(".bar")
            .data(data)
            .enter().append("rect")
            .attr("class",function(d) {
                return d.size < 0 ? "bar negative" : "bar positive";
            })
            .attr("x",function(d) {
                return x(Math.min(0,d.size));
            })
            .attr("y",function(d) {
                return y(d.name);
            })
            .attr("width",function(d) {
                return Math.abs(x(d.size) - x(0));
            })
            .attr("height",y.rangeBand())
            .append("title")
            .text(function(d) {
                return "This value is " + d.name;
            });
    ;

    svg.selectAll(".bar.positive")
            .style("fill","steelblue")
            .on("mouSEOver",function(d) {
                d3.select(this).style("fill","yellow");
            })
            .on("mouSEOut","steelblue");
            });

    svg.selectAll(".bar.negative")
            .style("fill","brown")
            .on("mouSEOver","brown");
            });

    svg.selectAll(".axis")
            .style("fill","none")
            .style("shape-rendering","crispEdges")
            .style("stroke","#000")
            .style("font","10px sans-serif");

    svg.selectAll(".grid")
            .style("fill","none")
            .style("stroke","lightgrey")
            .style("opacity","0.7");

    svg.selectAll(".grid.path")
            .style("stroke-width","0");

编辑：
请看看这个小提琴：
http://jsfiddle.net/GUYZk/9/

我的问题是可重复的.您不能使用rangeRoundBands更改outerPadding,而rangeBands表现正常.