High kilovoltage technique as compared with low kilovoltage in taking chest radiogram has much advantages. Authors performed an experiment by using acryl phantom to make the technical chart at 120KV and obtained the results as follows; 1. Increase and decrease of tube voltage in thickness change was 3.2KV per cm at variable technic chart. 2. At fixed kilovoltage technic chart, increase and decrease was $0.12{sim}0.2$ mAs per cm in chest thickness. 3. Increase and decrease of distance was 1.3inches per cm in thicknese change