In　order　to　study　the　extant　pre-stressed　force　in　the　pre-stressed　concrete　beam,　the　stress-releasing　method　on　the　pre-stressed　hollow　slab　beam　which　had　served　for　20　years　was　used　in　the　grooving　test.　The　effects　of　different　cutting　positions　and　cutting　gap　spacing　on　the　testing　stress　release　rate　are　researched.　The　variation　law　of　the　release　concrete　working　stress　with　the　changing　of　the　notch　depth　and　gap　spacing　in　the　grooving　test　was　analyzed,　achieving　the　depth　of　notch　when　the　working　stress　of　beam　concrete　was　release　completely.　The　fitting　function　between　the　cutting　depth　and　the　measured　residual　stress　was　established　using　numerical　analysis　software,　so　as　to　deduce　the　surface　initial　stress　of　the　beam　bottom.　According　to　the　derived　formula　of　existing　pre-stress　of　concrete,　the　initial　stress　generated　from　the　derivation　was　substituted　into　the　calculation　formula,　so　as　to　get　extant　pre-stress　of　the　beam.　By　this　method　the　extant　pre-stressed　force　of　beam　was　accurately　estimated.　This　paper　provided　reference　to　a　certain　extent　for　effective　pre-stress　evaluation　and　assessment　of　bridge　structure.