The Qingming Festival is in honor of Jie Zitui. During the Spring and Autumn Period, Jin Duke Chong Er was framed and exiled abroad, and it was difficult to find a livelihood. He fainted from hunger on the road, at this time, the attendant minister Jie Zi Pui cut a piece of meat from his own thigh and cooked a bowl of meat soup for the duke to drink, Chong Er gradually recovered his spirit, and when Chong Er realized that the meat was cut from Jie Zi Pui's own leg, he shed tears.
Nineteen years later, Chong Er became the king of the country, the historical Duke of Jin. But by this time, Jie Zi Pui, who used to give up his life to save him, had long been sick and died. In his honor, Duke Wen of Jin designated the day of his death as the Qingming Festival, which has been passed down to this day.
Expanded Information
The people of Jin banned fireworks to commemorate the death of Jie Zi Tui. They also used flour and jujube paste to make swallows, strung them up with willow sticks and inserted them above the door to summon his soul, which was called "Zhi Push Yan" (介子推, also known as Jie Zhi Pui). Since then, the cold food and Qingming became the grand festivals of the people all over the country.
Whenever there is a cold food, people don't make fire to cook and only eat cold food. In the north, the people only eat pre-made cold food such as jujube cake, wheat cake, etc.; in the south, it is mostly green dumplings and glutinous rice sugar lotus root. Every Qingming, people weave willow into a circle and wear it on their heads, and stick willow branches in front of and behind their houses to show their remembrance.
Reference:
Baidu Encyclopedia_Jie Zi Tui