Anhydrous ammonia is one of the medium where the steel is easy to suffer stress corrosion cracking. Many stress corrosion crack accidents of ammonia storage tanks have been reported all over the world for recent years. 16MnR low alloy steel with good composite mechanical properties is the most common used pressure vessel steel in China, it has better anticorrosion properties than the low alloy high strength steel, especially in anhydrous ammonia environments. Many stress corrosion crack researches have been done for 16MnR steel in wet hydrogen sulfide service for last decades, but less has been done in anhydrous ammonia environments. Stress corrosion tests with eight constant strain pre-cracked specimen were carried out in this work. The pre-cracked specimen were loaded with loading bolts and put into the special ammonia storage tank for tests, they were taken out from the tank periodically to measure crack length. The stress corrosion crack growth rate and the threshold stress intensity factors KISCC of 16MnR steel in anhydrous ammonia environments were measured. Based on test results, the effects of environmental factors and steel strength on stress corrosion cracking of 16MnR steel in anhydrous ammonia service were analyzed. It could be concluded that specimen cracks of the 16MnR steel in anhydrous ammonia environments almost do not grow, threshold stress intensity factors KISCC are higher than 90MPa m .