Qiangtang basin is recognized as advantageous prospecting area for natural gas hydrate and core drilling is the most direct and accurate method to identify natural gas hydrate. The technical methods of large diameter coring and core protection by low temperature mud were assigned to meet the requirements of natural gas hydrate drilling; trial production of simultaneous casing coring tool and large diameter wire-line coring tool were carried out; low temperature mud formula was gradually improved and new type efficient mud cooling device was developed. In the construction process of natural gas hydrate survey well in Yahu area, in spite of complex formations and bad environment, sample drilling construction was completed at final depth of 700.70m. The core samples can satisfy the geological requirements, the stratum lithology, thickness of frozen earth, gas source and physical properties of rock are found out, which provides geological data, technical support and talent reserve not only for the evaluation of natural gas hydrate resources but also for other oil and gas resources investigation.