Purpose: Simple part or equipment is necessary TRA(Technology Readiness Assessment) or MRA(Manufacturing Readiness Assessment). But sole maturity like TRA, MRA has limit complex systems or SoS(System of System). Especially complex weapon system need from the System Maturity Point of view. This research shows necessity of SRA(System Readiness Assessment). Methods: In case of complex systems, it is essential to SRA(System Readiness Assessment). For the purpose of calculating SRL(System Readiness Level), TRL and IRL must be calculated. And then SRL can obtain know from equation of TRL and IRL. To prove SRA effectiveness, it is calculated SRL of JTDLS(Joint Tactical DataLink System) programs. Results: SRA procedure is proposed and case study shows as examples of JTDLS programs. Although result of TRA is TRL6, result of SRA is not 0.6. From this research, we can know necessity of SRA. Especially complex systems or SoS(System of System) is essential to SRA. Conclusion: SRA(System Readiness Assessment) is required to overcome limitation of sole maturity and to achieve a successful acquisition of high quality weapon system. This research intended to suggest SRA procedure and case study in complex defense system.