DECLARE
  v_clob CLOB   :='but it have restriction in amount argument(4000).the 
length of column is more than 32767 in some rows.Is there any solution for that';
  amount INTEGER:=20;
  offset INTEGER:=1;
  LEN    INTEGER;
BEGIN
  LEN :=dbms_lob.getlength(v_clob);
  WHILE offset<LEN
  LOOP
    dbms_output.put_line(dbms_lob.substr(v_clob,amount,offset));
    offset:=offset+amount;
  END LOOP;
END;