Abstract: This paper aims at the specialties of the CNC programming. The fitting method of biarc is analyzed. A fitting algorithm of biarc is realized based on VB, and the deviation of the fitting is analyzed. The regularity of the deviation is explored by comparing the influence of factors on the error analysis. An improved fitting algorithm of biarc is put forward based on step planning.

Key words: biarc fitting, VB, error analysis, step planning