需要自定义LineChartRenderer，相关代码如下

public class MaximumLineBarRenderer extends LineChartRenderer {
    private float mMaxValue;

    public MaximumLineBarRenderer(LineDataProvider chart, ChartAnimator animator, ViewPortHandler viewPortHandler) {
        super(chart, animator, viewPortHandler);
    }

    public void setMaxValue(float maxValue){
        mMaxValue = maxValue;
    }

    @Override
    protected void drawCircles(Canvas c) {

        LineDataSet dataSet = (LineDataSet) mChart.getLineData().getDataSetByIndex(0);

        List<Entry> entries = dataSet.getEntries();
        //找出曲线中yValue值最大的点
        Entry maxYValueEntry = entries.get(0);
        for (Entry entry : entries) {
            if (entry.getY() > maxYValueEntry.getY()) {
                maxYValueEntry = entry;
            }
        }
        Transformer trans = mChart.getTransformer(dataSet.getAxisDependency());
        MPPointD pointD = trans.getPixelForValues(maxYValueEntry.getX(), maxYValueEntry.getY());

        mXBounds.set(mChart, dataSet);
        String content = (int)maxYValueEntry.getY() + "分钟";
        Paint bubblePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
//        bubblePaint.setColor(Color.parseColor("#244EA9FD"));
        bubblePaint.setStyle(Paint.Style.FILL);

        Paint textPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        textPaint.setColor(Color.parseColor("#4EA9FD"));
        textPaint.setStyle(Paint.Style.FILL);
        textPaint.setTextAlign(Paint.Align.CENTER);
        textPaint.setTextSize(Utils.convertDpToPixel(15));
        textPaint.setTypeface(Typeface.create(Typeface.DEFAULT, Typeface.BOLD));

        Rect rectTextBounds = new Rect();
        textPaint.getTextBounds(content, 0, content.length(), rectTextBounds);
        int contentWidth = rectTextBounds.right - rectTextBounds.left;
        int contentHeight = rectTextBounds.bottom - rectTextBounds.top;
        //文字左右和上下与气泡之间的间距
        int offsetX = (int) Utils.convertDpToPixel(10);
        int offsetY = (int) Utils.convertDpToPixel(5);
        //整个气泡区域中心对应坐标
        float centerX = (float) pointD.x;
        float centerY = (float) (pointD.y - contentHeight / 2 - offsetY - Utils.convertDpToPixel(5));
        //气泡区域的位置信息
        RectF rectF = new RectF(centerX - contentWidth/2f - offsetX,
                centerY - contentHeight / 2f - offsetY,
                centerX + contentWidth / 2f + offsetX,
                centerY + contentHeight / 2f + offsetY + 10);
        Bitmap bubble = BitmapFactory.decodeResource(((LineChart)mChart).getContext().getResources(), R.drawable.bg_growth_report_chart_maximum);
        c.drawBitmap(bubble, null, rectF, bubblePaint);

        Paint.FontMetrics metrics = textPaint.getFontMetrics();
        float top = metrics.top;
        float bottom = metrics.bottom;
        //气泡背景尖角的高度.px
        int bitmapCuspHeight = 10;
        int baseLineY = (int)(rectF.centerY() - bitmapCuspHeight / 2 - top / 2 - bottom / 2);
        c.drawText(content, rectF.centerX(), baseLineY, textPaint);
    }
}