DataGridViewComboBoxCell cb= new DataGridViewComboBoxCell();
//给下拉框赋值: dt包含ID和Name两列,也可以自己在属性Items里直接添加下拉框显示的每一项
cb.DataSource = dt;
cb.DisplayMember = "Name";
cb.ValueMember = "ID";
DataGridView.Rows[i].Cells[j]=cb;
DataGridView.Rows[i].Cells[j].ReadOnly=false;
方法很多 网上搜搜吧