In order to check the realizability of CNC system runtime logic and performance, technology of system dynamic modeling and analyzing based on net theory was introduced. A strategy of conditional equal-transformation of TTPN with inhibitor arc was proposed, which will descend the model dimension and decrease analyzing complexity. An analyzing model of the system motion control-associated processes was built, which was then transformed equivalently according to the foregoing strategy. With that model, a simulation was carried out and the quantitative basis for the system structure adjusting was given. Further simulation illustrates that the adjusted system is able to achieve expected performance.