if(System.IO.File.Exists(path))
    {
     goodsid+=dt.Rows[i]["goodsid"].ToString()+",";
//     if(!System.IO.File.Exists(Picpath))
//     {
      System.Drawing.Image img=System.Drawing.Image.FromFile(path);
      //生成中图
     int w=img.Width;  //当前图片的宽
     int h=img.Height;  //当前图片的高
     int x=0;           //设置生成图片的宽
     int y=0;           //设置生成图片的高
    int curx=182;
    int cury=122;
     if(w>=curx && h<=cury)
     {
      x=curx ;
      y=curx *h/w;
     } 
     else if(h>=cury&& w<=curx )
     {
      y=cury;
      x=cury*w/h;
     }
     else if(h>=cury&& w>=curx )
     {
      if(h/cury>w/curx )
      {
       x=curx ;
       y=curx *h/w;
      }
      else
      {
       y=cury;
       x=cury*w/h;
      }
     }
     else if(h<=cury&& w<=curx )
     {
      x=img.Width;
      y=img.Height;
     }
      System.Drawing.Image  newimg=img.GetThumbnailImage(x,y,null,new System.IntPtr(0));
      newimg.Save(Picpath,System.Drawing.Imaging.ImageFormat.Jpeg);
      img.Dispose();
      newimg.Dispose();

上面写的这个有些错误。。。
if(System.IO.File.Exists(path))
    {
     goodsid+=dt.Rows[i]["goodsid"].ToString()+",";
//     if(!System.IO.File.Exists(Picpath))
//     {
      System.Drawing.Image img=System.Drawing.Image.FromFile(path);
      //生成中图
     int w=img.Width;  //当前图片的宽
     int h=img.Height;  //当前图片的高
     int x=0;           //设置生成图片的宽
     int y=0;           //设置生成图片的高
    int curx=182;
    int cury=122;
     if(w>=curx && h<=cury)
     {
      x=curx ;
      y=curx *h/w;
     } 
     else if(h>=cury&& w<=curx )
     {
      y=cury;
      x=cury*w/h;
     }
     else if(h>=cury&& w>=curx )
     {
      if(h/cury<w/curx )
      {
       x=curx ;
       y=curx *h/w;
      }
      else
      {
       y=cury;
       x=cury*w/h;
      }
     }
     else if(h<=cury&& w<=curx )
     {
      x=img.Width;
      y=img.Height;
     }
      System.Drawing.Image  newimg=img.GetThumbnailImage(x,y,null,new System.IntPtr(0));
      newimg.Save(Picpath,System.Drawing.Imaging.ImageFormat.Jpeg);
      img.Dispose();
      newimg.Dispose();

这个修正后的