Seam-penetrating drilling hydrofracturing gas extracting method

Provided is a seam-penetrating drilling hydrofracturing gas extracting method. The method includes that a target drill hole and a hole for penetrating a coal seam are preset as a hydrofracturing free surface; a chambering section of the target drill hole is expanded, and a sleeve is put into the drill hole, fixed and connected with a separating chamber. High-pressure water enters the fracturing drill hole to fracture a coal body, and a fracturing gap is gradually expanded until the gap is communicated with the hole. The water pressure and water amount are increased, and the coal body around the gap is washed. Water flow carries gas and the coal body to pass through the target drill hole to enter the chamber, the gas is extracted, and separation of the gas is achieved. After the coal body is washed, a macro gap communicating the fracturing drill hole and the target drill hole is formed. During extraction, the gas leaks into the gap, flows into the target drill hole and the hydrofracturing drill hole, and a gas flowing mode is changed fundamentally. The gap is equivalent to extension of the length of the target drill hole and the hydrofracturing drill hole in the coal seam, contact area between the gap and the coal body is increased, and a gas extraction effect can be improved.