UN Secretary-General Antonio Guterres launched the funding drive at a conference in Geneva aiming to raise $2.96 billion (€2.4 billion) for this year.
Last year's Yemen appeal was for $2.5 billion, which was 73 percent funded, but the needs have intensified in a country battered since 2015 by a Saudi-led military offensive aimed at repelling Iran-backed Huthi rebels who control the capital.
"Yemen is the world's worst humanitarian crisis," Guterres said, calling the situation "catastrophic."
"But with international support, we can and must prevent this country from becoming a long-term tragedy," he said.
According to the UN, 8.4 million people are on the verge of famine in Yemen, where food imports are essential to sustain the population.
Saudi Arabia and its allies shut down the country's land, sea and air borders last year in response to a missile attack by the Huthis that was intercepted near Riyadh.
While the coalition has eased the blockade, restriction on deliveries persist.
"Humanitarians must be able to reach the people who need help the most, without conditions," Guterres said.
"All ports must remain open to humanitarian and commercial cargo, the medicines, food and the fuel needed to deliver them," he added.
About 10,000 Yemenis have been killed and 53,000 wounded since the start of the coalition intervention in Yemen.
The funding appeal came a day after several children were among those killed in a strike on the rebel-held port of Hodeida.
The UN called the incident "one of the deadliest attacks on children since the conflict in Yemen escalated in March 2015".
The coalition is the only force known to carry out air strikes on Huthi rebel-held territory and has previously admitted to "erroneous" strikes that caused civilian casualties.