The deformation and failure evolution process of rock slope during disaster incubation period is controlled by internal long fissures (controlling fissures), and the evolution mechanism is of great significance for the prevention of landslide disasters. Based on the transparent physical model experiment technology, two typical rock slopes with controlling fissures (one with a steep fissure in the upper part of slope and the other with a gently inclined fissure in the lower part) were selected as the objects, and the evolution process of deformation and failure inside the slopes was studied through physical model experiments using the self-developed equipment. The displacement rate and strain rate were taken as the characterization quantities of the deformation and fissure propagation, and the spatiotemporal evolution mechanism under the influence of fissures was analyzed with the reference of the common slope without controlling fissure. The conclusions are: (1) The reliability of the proposed experiment method in the study of the deformation and failure evolution process inside the slopes was verified through the simulation of internal deformation accumulation and progressive process of fissure initiation, propagation, and penetration. (2) The deformation and failure process of the slopes with controlling fissures is similar to that of the slope without controlling fissures and can be divided into four stages: deformation accumulation, failure band/fissure initiation, failure band/fissure expansion adjustment, and rapid expansion and penetration of failure bands/fissures. (3) The tip of steep fissure in the upper part undergoes a tensile-shear mixed initiation and expands downwards due to the pushing action induced by initial fissure slip deformation, while the tip of gently inclined fissure in the lower part undergoes tensile initiation and expands upward due to the traction induced by initial fissure slip deformation. The propagation rates of fissures increase exponentially with the increasing length of fissures. (4) The fissure propagation modes change with the evolution of slope deformation and fissure propagation. The steep fissure in the upper part starts to propagate in tensile-shear mixed mode and turns to propagate in shear mode, and finally shears out near the slope toe. The gently inclined fissure in the lower part firstly propagates in tensile mode and then transforms to shear mode, and finally intersects with the failure zone in the upper part.