The invention provides acyclic nucleoside phosphonate derivatives and their pharmaceutically acceptable salts represented by the formula disclosed in the specification, wherein R1 and R2 represent C1-C3 alkoxy and halogen (un)substituted alkoxy, C1-C3 alkyl and halogen (un)substituted alkyl, halogen, R3 represents hydrogen, C1-C3 alkyl and halogen (un)substituted alkoxy, C1-C3 alkyl and halogen (un)substituted alkyl, halogen, R1, R2, R3 are identical or different, R4 represents H or C1-C3 alkyl, R5 represents H, CH2CF3, OCH2-OOR6, OCOOR6, R6=straight chain or branched chain C1-6 alkyl.