Abstract: In order to analyze the characteristics of the multi-mass elastic torsion system,an estimation of the model is necessary. Hence,a fractional system identification considering the elasticity of the system and combining the advantages of the fractional system is implemented. Obtaining the fractional orders in time domain is not convenient. Hence,the fractional order model is obtained by considering the stochastic search pattern of the particle swarm optimization (PSO),and the PSO algorithm is used to identify the multi-mass elastic torsion system. In contrast,the integer system identification based on PSO is implemented as well. According to these results,the performance indicator of fractional system is better than that of the integer system,laying a foundation for analysis and control of the system.