Chlorination is a common method of water disinfection in the world, especially in developing countries. But this process can cause harmful compounds such as trihalomethanes. In this investigation, the importance of different levels of chlorination on aquaculture effluent (cold fish) to produce trihalomethane compounds (THMs) was determined. In this experiment, 400 liters of rainbow trout farm sevage were collected and transferred to Laboratory and divided into 15 containers with 20-liter capacity as experimental treatment. Then different concentrations of chlorine (sodium hypochlorite) were added to the containers, including five treatments (control), 10, 20, 30 and 40 mg / l. each treatment had 3 replications and shaker for ventilation. Experiment duration was 24 hours. The experiment result showed that the amount of trihalomethane increased with chlorination increasing. So that in the 40 mg / l chlorination treatment, the total trihalomethane concentration was 4 ± 82 μg / l but in the control treatment, was 15.2 μg / l. Also, although the mean of produced chloride-bromomethane did not show a significant difference between the experimental treatments (p> 0.05), the experimental treatments were significantly different compare with control treatment. Also, with increasing chlorination concentration, the compounds of dichlorobromethane and chloroform formed an increasing trend and the difference between treatments were significant, while different levels of chlorination had no effect on increasing the concentration of bromoform and the difference between treatments were not significant. The production of trihalomethanes in the process of aquaculture wastewater treatment due to the high level of organic matter in these effluents is higher than the global health standards, except in the 10 mg / l treatment. Therefore, due to the experiment results the maximum allowable concentration for process of aquaculture wastewater (cold-water fish), 10 mg per liter of liquid chlorine is recommended.