picturebox控件共有两种载入图片方式，分别为：
pictureBox1.BackgroundImage = Image，pictureBox1.load(url)
为使加载的图片自使用控件尺寸，可以分别对pictureBox控件设置BackGroundImageLayout=Stretch，SizeMode=StretchImagewinform中picturebox自适应图片大小
做了一个示例，代码如下，后面附完整项目源码下载：
using System; using System.Windows.Forms; namespace HoverTreePictureBox { public partial class Form1 : Form { public Form1() { InitializeComponent(); WindowState = FormWindowState.Maximized; } private void button_getPicture_Click(object sender, EventArgs e) { pictureBox_HoverTree.SizeMode = PictureBoxSizeMode.StretchImage; pictureBox_HoverTree.BackgroundImageLayout = ImageLayout.Stretch; try { pictureBox_HoverTree.Load(""); } catch (Exception ex){ MessageBox.Show("何问起",ex.Message); } } private void button_hovertreeZoom_Click(object sender, EventArgs e) { //图像大小按其原有的大小比例被增加或减少 by 何问起 pictureBox_HoverTree.SizeMode = PictureBoxSizeMode.Zoom; } private void button_HovertreeStretch_Click(object sender, EventArgs e) { //PictureBox 中的图像被拉伸或收缩，以适应PictureBox的大小。 by 何问起 pictureBox_HoverTree.SizeMode = PictureBoxSizeMode.StretchImage; } private void s_Click(object sender, EventArgs e) { //调整PictureBox的大小，使其等于所包含图像的大小 by 何问起 pictureBox_HoverTree.SizeMode = PictureBoxSizeMode.AutoSize; } } }