To　measure　the　components　without　nominal　geometrical　form　and　parameter,　the　＇form-free　measurement　mode＇　was　presented　in　this　paper.　To　accomplish　this　measurement　mode,　the　＇data　particulates＇　of　measurand　were　obtained　with　high　accuracy,　the　theoretical　models　of　typical　geometries　and　their　invariable　moments　were　set　up　as　the　principle　for　form　recognition,　the　nominal　form　of　measurand　was　recognized　according　to　the　principle,　and　geometrical　parameters　were　calculated　and　measurement　uncertainty　was　assessed　by　data　process　software.　Two　correlative　critical　aspects,　extraction　of　geometrical　information　and　recognition　of　form,　were　discussed.　The　extraction　techniques　of　geometrical　information　were　analyzed,　the　requirements　on　measuring　machine　were　clarified,　and　an　adaptive　sampling　method　combining　interpolation　with　extrapolation　techniques　was　introduced.　Six　fast　arithmetic　operators　for　geometrical　form　recognition　were　presented.　A　measuring　machine,　FormFree300,　was　fabricated　and　the　function　of　＇form-free　measurement　mode＇　was　realized.