Urea selective catalytic reduction is the most promising technique to reduce NOx emissions from heavy duty diesel engines. 32.5wt% aqueous urea solution is widely used as ammonia storage species for the urea selective catalytic reduction process. The thermolysis and hydrolysis of urea produces reducing agent ammonia and provides to catalysts to reduce NOx emissions to nitrogen and water. However, the application of urea SCR technology has many challenges at low temperature conditions, such as deposits formation in the exhaust pipe, lack deNOx performance at low temperature and freezing below -12℃. For preventing deposits formation, the aqueous urea solution is difficult to be injected into the exhaust gas stream at temperature below 200℃. The aqueous urea solution used as reducing agent precursor is the main obstacle for achieving high deNOx performances at low temperature conditions. This paper presents a solid SCR technology for deNOx emissions from heavy duty diesel engines.The solid SCR technology, using a solid metal ammine complex to store ammonia, can overcome the issues of urea SCR system by dosing gaseous ammonia directly to the exhaust pipe. In this paper, the applications of solid SCR system for a CN-5 heavy duty diesel engine and a CN-4 heavy duty diesel vehicle are discussed based on engine bench tests and portable emission measurement system tests, and comparison researches on NOx emission is made with urea SCR system. The results indicate that the solid SCR technology can promote the deNOx performances more efficiently than urea SCR technology at low temperature conditions, save cost of the aftertreatment system and have higher reducing agent economy.