The invention discloses a gas-slag separation device for drilling. The gas-slag separation device for drilling comprises two wall plates, a left side plate, a separation plate and a right side plate,wherein the two wall plates are symmetrical at the front side and the back side; the wall plates are of L-shaped structures and are fixedly connected through the left side plate and the right side plate; the separation plate is fixedly connected to the upper part of the middle of the wall plate; a horizontal cover plate is fixedly connected to the top ends of the wall plates, the left side plate and the separation plate; a gas-slag inlet pipe and a blowout control connecting pipe are arranged on the cover plate; a lower inclined plate of an arc-shaped structure is fixedly connected among the bottom of the left side plate, the bottom end of the right side plate and the wall plate; the right side plate is in inclined arrangement; a slag extraction device is arranged on the right side plate;and a slide plate is fixedly connected between the wall plates. Through the arrangement of the separation plate and the slide plate, gas and slag are separated in the flowing process; the slags are discharged through the slag extraction device; the gas enters an extraction pipe to be exhausted; an extraction pipe blockage phenomenon cannot occur; and a good effect is achieved.