Abstract: In order to determine the reasonable technological parameters in NC milling of deep-cavity and thin-walled part of high-precision, with the aid of dynamics simulation method for technological parameter optimization in NC machining and by means of establishing dynamic system experiment modal analysis testing platform for the milling process, dynamic characteristics of cutting tools with different length-diameter ratio on special machine tools can be tested. Then, the optimized cutting parameters for different characteristics of the cutting tools, specified machine tools as well as the cutting stabilization area of machining system at different cutting stages can be obtained. Consequently, material-removing rate of the part can be improved effectively; the phenomenon of tremble of the cutting tools owing to large length-diameter ratio in the cutting process can be suppressed. Thus, difficult problem of chatter mark on the wall of high-precision, deep-cavity and thin-walled box during milling process can be solved in a better way.