Abstract: FlexRay is becoming the in-vehicle communication network of the next generation. To resolve the problem of Frame IDentification (FID) assignment in the FlexRay Static Segment Scheduling (FSSS), an Automatic Model Coefficient Matrix Generating (AMCMG) algorithm is proposed to obtain the coefficient matrix automatically based on the characteristics of period distribution. A large-scale programming model of FSSS can be generated automatically, and the scheduling properties of all kinds of messages can be derived as well as the minimum number of FID required for the system can be determined quickly. To assign the phase for each message and obtain the complete scheduling table, a Phase Reserving based FID Assignment (PRFIDA) algorithm is designed according to the compatibility of messages scheduling in different periods, which is able to keep the optimal property of the previous programming. Finally, the simulation results demonstrate that the AMCMG algorithm can build the scheduling model rapidly and correctly, and the PRFIDA algorithm can realize the FID assignment optimally based on the known scheduling properties of messages.