The trade expo, which begins tomorrow, is being held at Kunming City in Yunnan Province, where Koirala has been invited as a special guest of honour by the government of China.
Koirala, leading a 33-member delegation, is being accompanied by Commerce Minister Sunil Thapa and other senior officials.
The expo being organised from June 6-10 is expected to boost Nepal's trade relations with China.
The prime minister is scheduled to inaugurate the expo tomorrow. Koirala will hold bilateral talks with Li Jiheng, governor of Yunnan Province later.
Nepal has been chosen as the "country of honour" at the event and will showcase its cultural heritage at a separate pavilion during the expo.
This is Koirala's second foreign visit after India. Koirala last week made a maiden trip to India as prime minister to attend the oath taking ceremony of Narendra Modi.