Govardhan Puja is performed on the day of Kartik Shukla Paksha Pratipada. According to Hindu mythology, Lord Krishna worshiped Govardhan Parvat on this day in Mahabharata. This tradition has continued since then.
Once upon a time Indra became proud of his powers. Then Lord Krishna created a play to crush their pride. In this, he saw all the Brajwasis and their mother preparing for a puja, then Yashoda asked the mother, "Mayya, who are you all preparing for worship?" Mata then tells him that "she is preparing to worship Indradeva."
Then Lord Krishna asked "Maia, why do we all worship Indra? Then Mayya told that 'Indra rains and from that we get food and grass of our cow. Hearing this, Krishna ji immediately said" Maia our cow If the grain grazes on Mount Govardhan, it should be revered for us. Indra Dev is arrogant, he never gives darshan.
Considering Krishna, all Brajvas worshiped Govardhan Parvat in place of Indradev. Enraged at this, Lord Indra started torrential rain. Seeing the rain taking the form of flood, all the residents of Braj started cursing Lord Krishna. Then Krishna ji lifted the Govardhan mountain on his Kani finger to protect the people from the rain.
After this, everyone was asked to take shelter with their cow under the mountain. This made Indra Dev more angry and increased the speed of rain. In order to break Indra's pride, Shri Krishna told Sudarshan Chakra that you stay on top of the mountain to control the speed of rain and make a rag from Sheshnag and prevent water from coming towards the mountain.
Indra Dev continuously showered night and day. After a long time, he realized that Krishna is not an ordinary human being. Then he went to Brahma ji, then he came to know that Shri Krishna is none other than Shri Hari himself as an incarnation of Vishnu. On hearing this, he went to Shri Krishna and started apologizing to him. After this Devaraj Indra worshiped Krishna and offered them as an offering. Since then, the tradition of Govardhan Puja has been maintained. It is believed that Lord Krishna is pleased by worshiping Govardhan Parvat and cows on this day.