The invention provides an acidizing method for a horizontal well in a carbonate rock reservoir. The acidizing method includes the steps that S1, acid liquor is injected into the horizontal well, the injection flow is 0.5 m<3>/m to 3 m<3>/m; S2, fiber-foam base VES acid is injected, the injection flow is 0.3 m<3>/m to 1.5 m<3>/m; and according to the length of the horizontal well, the process of the first step to the second step is circulated every 60 m to 100 m horizontal section length of the horizontal well to complete acidizing of the horizontal well in the carbonate rock reservoir. According to the acidizing method for the horizontal well in the carbonate rock reservoir, the acidizing effect of the horizontal well can be significantly improved, and no damage to the reservoir is achieved.