Dynamic　tracing　and　trace　replay　are　two　main　functions　in　vehicle　monitoring　system　of　GIS.　Based　on　the　idea　of　line-to-point　set,　＂point-to-point＂　road　matching　algorithm　and　＂Trace　interpolation＂　trace　replay　algorithm　are　designed　and　implemented.　The　main　idea　of　＂Point-to-point＂　is　that　the　road　will　be　separated　into　a　series　of　discrete　set　points,　and　then　got　path　matched　accordingly.　At　the　same　time,　prediction　principle　is　used　to　solve　problems　such　as　miscarriage　of　justice　at　the　crossroads;　First　of　all,　the　premise　of　applying　＂Trace　interpolation＂　is　studied,　and　then　the　process　of　algorithm　will　be　introduced.　It　reduces　the　cost　of　the　positioning　through　reducing　the　number　of　positioning　points;　Applied　to　actual　projects,　＂Point-to-point＂　achieves　a　high　accuracy　measures,　particularly　at　road　intersections.　It　improves　the　accuracy　of　cellular　positioning　greatly.　Similarly,　the　＂trace　interpolation＂　has　greatly　reduced　the　cost　of　positioning　and　is　proved　to　be　practical.