You can make a subquery with that INNER JOIN
and use DISTINCT
SELECT MID,NAME,SEX,AGE,RFM.TITLE,RFM.NAME ,PV.RFMID
FROM MMASTER
INNER JOIN AMM ON MMASTER.MID=AMM.MID
INNER JOIN PS ON AMM.AMMID=PS.AMMID
INNER JOIN PV ON PV.VTID=PS.VTID
INNER JOIN
(
SELECT DISTINCT RFMID, NAME
FROM RFM
) RFM
ON RFM.RFMID=PV.RFMID
INNER JOIN PM ON PV.PMID==PM.PMID
INNER JOIN SM ON PS.SMID=SM.SMID
WHERE PM.PMID='13'