There are two reason mainly, one is opium trade and another is exchange of unequal value between Chinese and foreign currency.

Under the British colonial rule, the opium trade was a major trade in Hong Kong from the early 1840s to the early 1940s, experiencing the three stages as: the transit trade by opium trader to other parts of China; a monopoly leased to the highest bidder and the government monopoly.

Legalization of opium trade refers to an international trade with opium as commodity,permitted by the customs specific supervisory institutions of foreign trade in the sovereign state and listed in a regular trade bill and collected a certain proportion of customs.

In Guo s opinion, the opium which had brought about great disaster to Chinese should be banned, the opium trade should be restricted and suppressed by the .

Rapid Analysis of Opium by Gas Chromatography;

An Exploration of the way inputting opium into Southeast of Guangxi in modern times——One of narcotic series papers;