The DEC, representing 13 aid charities, says Yemen is at "breaking point", with children dying from malnutrition.
The appeal, fronted by television presenter Clare Balding, is being launched on TV and radio on Tuesday.
Yemen has suffered 20 months of conflict, with Saudi Arabia backing the government against Houthi rebels.
The DEC said: "In the midst of conflict, DEC member charities are reaching millions of people across the country with lifesaving aid - but much more needs to be done."
The DEC represents 13 UK aid charities including British Red Cross, Oxfam, Save The Children and Christian Aid.
Clare Balding, who presents the appeal with actor Tom Hardy, said: "In recent days on the news we have seen the human cost of the civil war in Yemen.
"Images of babies so weak their limbs are like brittle sticks, and their eyes are sunk deep in their faces.
"Yemen has always been desperately poor but there are now half a million starving children."
The British Red Cross said: "The ongoing conflict in Yemen has devastated millions of people's lives.
"Right now, more than half the population don't have enough food. Almost a quarter face starvation. Families are living with no water or electricity."
The charity said vital support could be given to people in desperate need with the help of the British people.
It said 14 million people did not have enough food, and 3.3 million mothers and children were acutely malnourished.
Less than half the country's health facilities were functioning fully and they faced severe shortages of medicines, equipment and staff, it added.
Save the Children worker Alice Klein said families she saw in Yemen were "desperate".
"The babies and children were severely malnourished - as soon as the doctor began examining them and lifting up their clothes you could see all their ribs jutting out," she said.
She had "honestly never seen anything like it" but had seen aid make a "physical and tangible difference".
The appeal comes after Foreign Secretary Boris Johnson said he had "deep concern" about the suffering of Yemenis but understood the Saudi Arabia-led military intervention in the country.
TV and radio stations broadcasting the appeal include the BBC, ITV, Channel 4, Channel 5 and Sky.
A major appeal for help for millions of people facing hunger in war-torn Yemen is being launched by the Disasters Emergency Committee.