In the process of static parameters detection of artillery pipe, it is very important for the parameters of rifling to be recognized and extracted. The paper analyzes in detail the measuring principle, and also introduces the measuring process of the system. An algorithm is also developed based on class variance after a great number of cannon barrel images are analyzed. The verification in actual measurement shows that the algorithm satisfies the measurement precision indices and is in common use. Finally, analysis of the system and experiment result for uncertainty is given.