pb1[j] = new PictureBox();
pb1[j].Image = img;
pb1[j].Tag = str;
pb1[j].Name = j.ToString();

------解决方案--------------------
int total = 0;  
       private void button1_Click(object sender, EventArgs e)  
       {  
           OpenFileDialog op = new OpenFileDialog();  
           if (op.ShowDialog() == DialogResult.OK)  
           {  
            
               PictureBox p = new PictureBox();  
              //new add
               p.tga=op.FileName;
               p.Click += new EventHandler(p_Click);

               p.SizeMode=PictureBoxSizeMode.Zoom;  
               p.BackColor=Color.Black;  
               p.Image = new Bitmap(op.FileName);  
               p.Width=50;  
               p.Height = 50;  
               int x=(total%5) *60;  
               int y=(total/5) *60;  
               p.Location=new Point(x,y);  
               this.panel1.Controls.Add(p);  
               total++;  
           }  
       }


 void p_Click(object sender, EventArgs e)
       {
           string filenames = (string)((PictureBox)sender).Tag;
       }