In which month does the underground frozen layer not exist in Daqing every spring?

April. There is no underground frozen layer in Daqing every spring and April, and the depth of frozen layer is between1.7m-2.5m.. Anniversary, also known as Oil City, is a prefecture-level city under the jurisdiction of Heilongjiang Province, an important national oil production and petrochemical industrial base approved by the State Council, and an important regional central city in western Heilongjiang.