In　order　to　study　the　extant　pre-stressed　force　in　the　prestressed　concrete　beam,　the　test　was　using　the　stress-releasing　method　on　the　prestressed　hollow　slab　beam　which　was　served　20　years.　To　study　the　effects　of　different　cutting　positions,　cutting　gap　spacing　on　testing　stress　release　rate;　analysis　of　the　variation　law　of　the　release　concrete　working　stress　with　depth　of　notch　changes,　got　the　depth　of　notch　when　the　working　stress　can　release　of　all;　to　establish　the　fitting　function　realization　between　the　cutting　depth　and　the　measured　residual　stress,　To　achieve　the　accurate　prediction　of　existing　prestressed　beam.　In　order　to　provide　some　reference　for　the　effective　prestress　evaluation　and　assessment　of　bridge　structure　methods.