The invention provides a horizontal segment blast cracking and chemical weakening method for igneous rock in a thick coal seam. The method comprises the following steps: forming water injection drilling holes and a plurality of V-shaped grooves on one sides, close to working surfaces, of a tail entry and a haulage entry; carrying out a sampling test on the igneous rock, configuring a corresponding chemical solution, and determining the concentration, solution injection volume and solution injection time of the chemical solution; and then carrying out charging, stemming and sealing, and connecting a detonating cord for blasting. According to the invention, a physical method and a chemical method are combined, so that the general problem of difficult pushing of the igneous rock in the coal seam of the existing coal mine is solved; and the process is simple, the cost is low, the benefit is good, and the safety production of the coal mine is realized to the maximum extent.