I have store a news data(like 500 words)

When you create the table you have to define a column length that is long enough to store the data you're going to insert. Seems that the column you're trying to insert into is limited to 128 characters only.

To change the column length in the table you can use ALTER TABLE[^] command. So something like:

ALTER TABLE MyTableName ALTER COLUMN MyColumnName nvarchar(MAX);

String sql = "INSERT INTO News ( Category,Matter,Subject,date ) VALUES  (@Category,@Matter,@Subject,@date)";
       SqlCommand cmd = new SqlCommand(sql, con);
       cmd.Parameters.Add("@Subject", SqlDbType.VarChar, 100).Value = txtsub.Text;
       cmd.Parameters.Add("@Matter", SqlDbType.VarChar, 8192).Value = txtnews.Text;
       cmd.Parameters.AddWithValue("@Category", dropdwncate.SelectedValue);

String sql = "INSEART INTO News( Category, Matter, Subject,data)VATUES
<@category,@mater,@subject,@data)";>
Sql Command cmd = new Sql Command(spl,com);
cmd. Parameters.Add("@subject", Sql Db Type.Varchar,500).Value=txtsub.Text;
cmd.parameters.AddWithValue("@Category", dropdwncatedValue);