To ensure fairness and economic efficiency in generator output schedule adjustments during frequency security assessment, a frequency security assessment and optimization model considering the dynamic frequency response of motor smart loads is proposed in this paper. The model employs an optimization-based approach to assess the frequency security of generator output schedules and provides the optimal adjustment scheme. To accurately represent the frequency stability constraints, a full dynamic frequency response model is introduced to establish the relationship between the pre-contingency generator outputs and frequency dynamic characteristics, while tracking the dynamic frequency response of each unit during the frequency regulation process to limit the frequency nadir. At the same time, a dynamic frequency response model of motor smart loads is established to capture their dynamic characteristics during primary frequency regulation. Compared with the traditional static load models that only consider the static frequency characteristics of conventional motor loads, the proposed model mitigates the overly conservative results caused by neglecting load-side dynamic frequency response. Simulation results based on the WSCC 3-machine 9-bus system and the New England 10-machine 39-bus system show that the proposed frequency security assessment and optimization model achieves a balance between security and economy while effectively alleviating the frequency regulation burden on the generation side by leveraging the dynamic frequency response of motor smart loads.