In The Longest Day In Chang'an, Cao Poyan, as the main villain in the early stage, left a deep impression on everyone. However, the play only tells us that he is a wolf guard from the western regions, but does not name his specific identity. In fact, this point is stated in the first chapter of the original book: the applicant is Cao Poyan, a Sogdian, from Kangguo. This time, I came to Chang 'an with fifteen escorts, fifteen camels and a stallion. The goods I carried were thirty wool carpets and variegated leather goods, and all the way to Guanjin was checked and signed by the official. ? As for the image of Cao Poyan, the original work says: Cao Poyan is about thirty years old, with a high nose and deep eyes, and a thin chin with a hard black beard, like a hard bristle brush. If you count the white pointed felt hat he wears, the whole person must be more than seven feet tall.

At the beginning of the play, Cao Poyan's whiskers, black beard and pointed felt hat are shown, but unfortunately the actors are not high-nosed and deep-eyed.

The Sogdians are an Iranian-speaking people living in the middle of Central Asia, and their ancestors were nomads who moved from eastern Iran from 2 BC to 1 BC. "Sogdian" means "Suguda" in ancient Persian, and this name comes from the "Sogdian" province established by ancient Persian cyrus the great in the middle of Central Asia in the 6th century BC.

Since the Han Dynasty, the Sogdians have been the important middlemen of East-West trade on the ancient Silk Road. They successfully established a huge trade network between the Eastern Roman Empire, India and China, and even made Sogdian a common language on the ancient Silk Road. During the Northern Dynasties, with the decline of Guishuang Empire, many small countries were formed in Sogdian area, which was called "Zhaowu Nine Surnames Country" in China history books. Among the nine surnames in Zhaowu, Kangguo is the largest and the patriarch of other countries, and Cao Poyan comes from Kangguo.

the state of Kang is called "Sa-Mo Building" in The Tale of the Western Regions of the Tang Dynasty, and it is written that the capital of the National University is more than twenty miles in a week, which is extremely dangerous and solid, and it is crowded with people. Different treasures, gather more in this country. The land is fertile, the crops are planted, the trees are lush, the flowers and fruits are luxuriant, and there are many good horses. Clever skills, special agents. The gas order is smooth and the customs are fierce. ?

Since the 4th century AD, the Sogdians have continuously settled in Turpan, Hexi Corridor, Chang 'an and Luoyang. Especially with the Arab conquest of the Sassanian dynasty in Persia in 651 AD, and then the conquest of the Sogdian region in 712, the number of Sogdians who moved eastward to the Tang Dynasty increased greatly. It was during this period that Cao Poyan came to Chang 'an in 744 AD (Tianbao three years).

The ancient China exhibition of Guobo unearthed the epitaph brick of "Zhainaning's faint mother Kangbomiti" in 664 AD from the ancient tombs in Astana, Turpan. The owner of the tomb was Cao Poyan's hometown and a Sogdian from Kangguo. The epitaph uses Chinese characters but writes from left to right.