The two nations had a "deep and firm" friendship, Mr Xi said in an article in Zimbabwe's state-run Herald newspaper.
Zimbabwe's President Robert Mugabe has strongly pursued a "Look East" policy since the West isolated him over his controversial land reform programme.
China is major investor in Zimbabwe, helping to keep its economy afloat.
The BBC's Brian Hungwe in the capital, Harare, says President Mugabe was at the airport to welcome the Chinese leader, who received a 21-gun salute before inspecting a guard of honour.
Chinese nationals, waving both Zimbabwean and Chinese flags, were also there to welcome Mr Xi.
The two governments are expected to sign agreements to boost Zimbabwe's agriculture, mining and manufacturing sectors.
Mr Xi, who is on his first visit to Zimbabwe, said it remained a cornerstone of China's foreign policy to consolidate its relationship with Zimbabwe and other African states.
"This will never change," he added.
Mr Xi and a large Chinese delegation will fly to South Africa on Wednesday, where he will attend the first China-Africa summit to be held in Africa. It is expected to be attended by leaders from across the continent.
Analysis: Brian Hungwe, BBC Africa, Harare
For a government desperate for foreign direct investment and struggling to raise revenue Mr  Xi is a welcome guest.
I am told there are several bid deals, spanning manufacturing, agriculture and mining, waiting to be signed.
But what worries some is that such deals have been signed before and nothing tangible has materialised.
Government sources say the Chinese are hesitant to pump money into Zimbabwe because of its uncertain political climate.
President Mugabe is turning 92 in three months and the Chinese want guarantees that their investments will be safe if there is a change in leadership.
China's President Xi Jinping has arrived in Zimbabwe, making him the most prominent global leader in many years to visit the country.