Experimental power reactor (RDE) is a helium gas cooled high temperature reactor which is under development and proposed to be constructed in Indonesia. To assure its safety and reliability many safety features are applied to this reactor design including the use of digital based I&C and Reactor Protection System (RPS). Reliability of the computer based RPS will depend on both hardware and software embedded in the system. Hence the impact of the applied software on reliability and safety must be considered. This paper discusses the process in determining software requirement specifications which is one of the important stages in a software development lifecycle. The requirement analysis process is conducted based on some standards such as IEC-60880, IEEE-1233 and IEEE-830. System Requirement Specifications (SyRS) and Software Requirement Specifications (SRS) for designed digital RPS software have been generated and defined in the analysis. Further analysis would be necessary to provide more detail information on SRS. The software requirements obtained in this study become essential information for conducting further activities in the software development of computer based RPS.