Planar　enveloping　hourglass　worm　(TP　worm)　with　better　load　capacity　and　transmission　efficiency　is　a　type　of　transmission　superior　to　traditional　cylindrical　worm.　It　could　be　used　to　lightweight　design.　As　the　flank　of　the　worm　is　a　complex　toroidal　surface,　higher　demands　are　needed　for　the　manufacture　and　the　assembly.　This　paper　proposes　a　new　principle　to　adjust　the　processing　precision　of　the　worm.　The　principle　is　based　on　the　research　on　the　influence　of　the　parameter　errors　on　the　deviations　of　the　feature　lines　on　the　flank.　With　different　types　of　parameter　errors,　the　shape　and　the　value　of　the　deviation　curves　of　the　feature　lines　are　different.　At　last,　two　cases　are　introduced　to　verify　that　the　principle　could　be　used　to　improve　the　precision　of　the　TP　worm.