Exact solid-modeling of worm gears is very important for computer aided analysis，the model precision directly influences the accuracy of the subsequent CAE analysis. Aimed at the problem，a method for exact solid-modeling of double pitch ZN-type worm gears is presented based on meshing theory. Firstly，the paper analyzes the forming principle and characteristics of double pitch ZN-type worm gears and then deduces the mathematical equations of double pitch ZN-type worm gear；secondly，gear tooth working surface and boundary surfaces of worm gears are reconstructed by NURBS surface interpolation；finally，the three dimensional solid model of double pitch ZN-type worm gears is generated by trimming and stitching the surface. Error analysis shows that the geometric error of double pitch ZN-type worm gears established by this method is minimal，and it can meet the requirements of the subsequent CAE analysis，and proposes a new thought for the complex structure design of worm gears.