[Naeini1] The current research aims to investigate improvement possibility of Iran Heavy Diesel (DESA) Company Assembly Line by Simulation. Therefore, in addition to reviewing the existing thematic literature in relation to the system, model, simulation, assembly lines and the improvement solutions, as well as studying similar research background and history, the primary model of company assembly line was created by using data collection instruments like documents reviewing and observation. After presentation of created model and a summery of descriptive data, the model was validated by averages test. Data were analyzed by ARENA and SPSS using software. In the next stage, the improvable point of assembly line, namely Test room was identified by interviewing with 48 people related with assembly line. Then, after describing the reason of attention to this point, the use of new technology was proposed for achieving improvement in this section. The results of testing this proposition by simulation model showed that if such system is implemented in assembly line, the cycle time will improve by 33% and the queue time in test station will reduce by 62%. Finally, based on these results, the discussion and conclusion were represented, and some suggestions were given for managers and directions for further researches were provided in conclusion.