The SY is China's standard industrial steam locomotive. Over 1,800 of these useful light 2-8-2s were built between 1960 and 1999, the vast majority at Tangshan. Two prototypes were also constructed by Sifang (Qingdao) while Tongling, Jinan and Changchun also produced small batches.

Although the class is notable for being the last type in series production anywhere in the world, the basic design dates back to the 1920s. The SY is derived from the Japanese-built Mi Ka Ro design introduced to China by the Japanese occupiers in 1934 and better known by it's modern Chinese classification, JF6. The Mi Ka Ro was itself based on a series of ALCo locomotives supplied to Japanese-occupied Korea in the 1920s. Most classes developed by China post-liberation were heavily influenced by Soviet practice but the SY retained it's classic American appearance. This almost certainly influenced the decision of several US tourist railroads to acquire brand new SYs in the 1990s, around 70 years after their predecessors emerged from ALCo's works.

Most SY have retained their allocated numbers but some have been renumbered locally. Best known are the Benxi Steelworks fleet which carry numbers in the SY7xx series. Thanks to the diligence of a few recent visitors many of these have now been identified from stampings on various components. The 7xx numbers in the Benxi list have been cross referenced to the original numbers in the main list where these are known. Wuhan steelworks also renumbered its locos with SYs occupying the 5xx series. There have been no reports from Wuhan for many years and few of the original identities have been ascertained.

Several hundred SY remain in service in 2004, principally in the coal and steel industries, and the class can still be found at work in most parts of China. SYs aren't restricted to shunting service and can often be seen hauling freight and even passenger trains on local railways and extensive industrial systems.

At first sight, the SY is similar in appearance to the JF heavy mikado, hardly surprising as both classes share the same ALCo ancestry. The JF is, however, a much bigger engine with a noticeably fatter boiler. YJ and PL2 class 2-6-2s are also remarkably similar in appearance to SYs, sharing many principal dimensions. The SY's most distinctive feature is its slope backed tender, a design inherited from a small batch of JF6 intended for shunting services. The prototype SYs were fitted with a tender of more conventional design and the PL2 class 2-6-2s were equipped with a similar, but smaller, slope back tender so it isn't a 100% reliable indication that a particular loco is an SY.