The invention relates to a technology for fishing oil under pressure. According to the technical scheme, the technology comprises the following steps: 1, fixing a blowout preventer and a blowout prevention pipe on a flange at the bottom of a wellhead by installing the wellhead on site, connecting a gas receiving pipeline on a cover of an oil fishing well, and leading gas in the well into an oil conveying pipeline between an oil well and an oil production station through the gas receiving pipeline so as to reduce the gas pressure of the oil fishing well; 2, turning off the blowout preventer before fishing oil to prevent the high-pressure gas in the oil well from being communicated with the outside, and disassembling the gas receiving pipeline and the cover of the oil fishing well to enable the blowout prevention pipe to be communicated with the atmosphere to enable the pressure of the blowout prevention pipe reaches normal pressure. According to the technology, the purpose that under the condition that gas of a casing pipe in the oil fishing well is abundant and cannot be discharged, normal oil fishing production can be realized is achieved, the well blowout accidents occurring during the assembly and disassembly of wellhead devices are avoided, and the environmental pollution produced in the gas discharge process is avoided. The defects that normal oil fishing production cannot be realized, as gas of the casing pipe in the oil fishing well is abundant and cannot be discharged, the well blowout accident may occur when the wellhead devices are assembled and disassembled, and the environmental pollution is produced in the gas discharge process are overcome.