Quda (渠答) is an ancient military literature word, many military books and dictionaries of past dynasties interpreted Quda (渠答) as Tiejili (铁蒺藜). Some scholars have raised objections to this, believing that Quda (渠答) and Tiejili (铁蒺藜) are not the same thing. However, the specific shape of Quda (渠答) has always been controversial. The paper argues that Qu (渠) and Da (答) are two kinds of city guard instruments, Qu (渠) is a large wooden shield, Da (答) is also written Da (荅), which is a protective curtain made with straw and bamboo. Da (答) covers the Qu (渠), so Qu (渠) and Da (答) are often associated, the words Qu (渠) and Da (答) in the literature have evolved into a polysyllabic word, which refers to the facilities of guarding the city against the enemy. Quchan (渠幨) is also written Quzhan (渠譫), Chan (幨) is a protective curtain made of cloth. Quzhan (渠幨) and Quda (渠答) are made of different materials, however, after generalization, the two meanings are close to each other.