How to save the data of dynamically created textbox on clicking the save button?

Try this:

//get from db and put text-box dynamically as below:

Database object loop{
           TextBox new_textbox = new TextBox();
           new_textbox.ID = "txt" + 1;
           new_textbox.Text = "";
           PlaceHolder1.Controls.Add(new_textbox);
          }

When you click submit button then need to get value of all text box, so for that again do same as above:

Database object loop{
           TextBox tb = (TextBox)PlaceHolder1.FindControl(dbobject.[name]);
           string str1 = tb.text;

       }