To　clarify　or　interpret　the　measurement　results　of　double-flank　gear　measurement　(DFGM),　the　mathematical　model　of　radial　and　tangential　error　analysis　of　double-flank　gear　measurement　is　established.　Using　differential　method,　the　mathematical　model　of　surface-to-surface　contact　stage　is　concerned,　and　also　the　tip-to-surface　interference　stage　is　involved.　The　error　sources　including　the　base　radius　error　(or　profile　slope　deviation)　and　the　tooth　space　angle　error　(or　single　pitch　deviation)　of　the　gear　to　be　measured　are　concerned.　A　case　study　of　the　gear　parameter　with　the　gear　contact　ratio　1.77　is　discussed　to　explain　the　tooth　contact　process,　in　which　the　critical　contact　points　are　listed　for　determining　the　rotation　angle.　The　radial　and　tangential　composite　deviations　are　simulated　under　different　sign　combination　or　different　value　of　the　error　sources　to　cover　as　many　results　as　possible.　The　simulation　results　are　compared　with　the　measurement　results　on　a　gear　measuring　device　(GMD)　using　double　flank　rack　probe　(DFRP),　whereby　the　simulation　parameters　are　determined　through　the　gear　profile　slope　deviation　and　the　single　pitch　deviation　of　the　gear　measured　on　a　Gear　Measuring　Center　Klingelnberg　P26.　The　curves　of　the　simulation　results　and　the　measurement　results　on　GMD　are　consistent　to　each　other.　For　gear　grade　6　according　to　ISO　1328-1:2013,　the　allowable　value　of　the　total　profile　deviation　is　11.5　mu　m.　The　simulation　results　are　compared　with　the　measurement　results　on　a　gear　measuring　device　(GMD)　based　on　double　flank　rack　probe　(DFRP).　The　difference　between　the　peak　to　peak　value　of　the　simulation　results　and　the　mean　line　of　the　measurement　results　within　the　evaluation　range　is　1　inn　in　radial　direction　and　1.3　mu　m　in　tangential　direction,　which　means　the　simulation　results　has　better　consistency　with　the　measurement　results.　The　radial　and　tangential　error　analysis　of　DFGM　can　not　only　be　used　in　simulation　of　the　results,　but　also　in　interpreting　the　DFGM　measurement　results,　which　is　helpful　for　gear　measurement　and　quality　control.