There is growing national concern about the effects of exposure to radioactive substances such as rainwater and cooling water mixed with high concentrations of radioactive materials on the human body and marine ecosystem. The research and monitoring studies on marine ecosystem toxicity assessments in comparison to exposure to radioactive contaminated water are very limited. The aim of this study is to conduct a marine environmental assessment of radiation exposure, which has a very limited scientific basis due to toxicity assessment by exposure scenario, using a multi-faceted toxicity assessment method to identify potential impacts. In addition to marine ecosystems, tritium is continuously detected in residential areas near nuclear power plants, and is being released into the environment according to the allowable amount by country. However, there is a severe lack of scientific evidence on the impact of the allowable amount on environmental species. Since the annual tritium discharge can expose non-human species as well, it is necessary to continuously conduct impact assessments through various approaches on environmental species. Studies on the toxicity of tritium (a radioactive nuclide) in mammals and humans (genotoxicity, carcinogenesis, reproductive traits, etc.) have been conducted since the 1960s, but studies evaluating the effects of long-term exposure to low and high doses in the natural environment (freshwater and seawater) are very insufficient. In this study, we exposed cnidarian, soft coral to a variety of concentration of tritium and extracted its RNA. The differentially expressed genes are explored comparing with non-exposed control group corals and tritium-exposed corals after de novo RNA sequencing. We picked 3 clusters of genes including immunity process, metabolic process and antioxidant responses and traced the gene expressions in the exposed groups with low-high concentrations and 24- 48 hr exposure durations. And also bioconcentration Factor (BCF) was evaluated by measuring the extent to which radioactive nuclides (tritium) accumulate in the body of test organisms exposed to them. The results of the study could make it possible establishment of a system for environmental monitoring (diffusion, concentration, type, etc.) and biological impact assessment of radioactive water in radioactive contaminated water discharge areas.