The visit, Xi's first since 2016, will conclude a three-nation Southeast Asian tour that included stops in Vietnam and Malaysia.
Cambodian Prime Minister Hun Manet recently described Beijing as "an important and indispensable friend of Cambodia that has helped support the country's economic and social development".
Xi was greeted on Thursday at the airport in Cambodia's capital, Phnom Penh, by King Norodom Sihamoni.
During his visit, Xi is also scheduled to meet Prime Minister Hun Manet and Senate President Hun Sen, who is Hun Manet's father and predecessor as prime minister.
Trade will likely be a major topic of Xi's discussions in Cambodia, which faces among the highest tariff rates proposed by Washington.
In addition to Trump's universal 10 per cent tariff, the country faces the threat of a 49 per cent tax on exports to the U.S. once his 90-day pause expires.
As well as discussions on strengthening bilateral ties and regional and international issues, several agreements are expected to be signed on cooperation in various sectors.
In both countries, Xi emphasised strengthening ties, particularly in trade and investment, amid global economic uncertainties and the backdrop of trade tensions with the United States.
He underscored the need to oppose unilateralism and protectionism and uphold the multilateral trading system.
China is presenting itself as a source of stability and certainty as Southeast Asia scrambles to respond to tariffs imposed by US President Donald Trump, which threaten the region export-oriented economies whose largest markets are generally the United States.
The visit comes on the 50th anniversary of the April 17, 1975 takeover of Cambodia by the communist Khmer Rouge, which imposed a reign of terror with Maoist-inspired policies that saw an estimated 1.7 million Cambodians die of starvation, overwork or executions.
Beijing was the main foreign backer of the Khmer Rouge and supported the group in carrying on a guerrilla war after it was ousted from power in 1979 by an invasion from Vietnam, though such history is rarely discussed by either country.
Cambodia's rapid growth in recent decades has been fuelled largely by Beijing.
In Hun Manet's remarks earlier in April at the inauguration of a Chinese-funded road, he called China "a first-class partner country".
He pointed to achievements such as the inauguration of the Chinese-named Angkor Siem Reap Airport and a Phnom Penh ring road named after Xi as evidence of continued strong relations and gratitude.
China is Cambodia's largest trading partner, surpassing $US15 billion ($A24 billion) in 2024 and representing nearly 30 per cent of Cambodia's total trade volume, though greatly in Beijing's favour.
28°C