It's not very efficient, it's better to write a procedure to handle it if you have a large amount of data.

UPDATE T_PARTY_GRADE T1

SET T1.GRADE_TYPE= (select GRADE_TYPE from T_GRADE T2 WHERE T1.PARTY_ID=T2.PARTY_ID) ,

GRADE_LEVEL = (select GRADE_LEVEL from T_GRADE T2 WHERE T1.PARTY_ID=T2.PARTY_ID)