Coal seam often disappears or thinner than expected in coalfield drilling construction; therefore, the sampling experiment and the evaluation on minefield would be uncertain. In this case, the supplementary coal coring by slant drilling is necessary for accurately realizing the position and the thickness of coal seam with complete coal sample. Diamond wire-line coring drilling technology was adopted in the drilling construction in Dacun coalmine section of Guxu mining area of South Sichuan coalfield, the technology of supplementary coal coring with eccentric wedge was studied and mastered.