The invention belongs to the technical field of mechanical test equipment and method, and relates to a double-tool-rest reliability test device based on combined loading. The double-tool-rest reliability test device comprises two tool rests, a double-tool-rest mounting table device, a combined loading device, a control cabinet, a data acquisition box, and a control console. The two tool rests are mounted on the double-tool-rest mounting table device, and are driven by a servo motor to move along a guide rail. The combined loading device is disposed on the double-tool-rest mounting table device and arranged between the two tool rests, and are used for applying a load to the two tool rests at the same time and detecting the performance of the tool rests. Switching between an ordinary tool bit loading mode and a dynamic tool bit loading mode is realized by means of hierarchical automatic switching, wherein ordinary tool bit loading is based on a direction-adjustable piezoelectric ceramic loading mechanism, and dynamic tool bit loading is based on the mutual support principle of two dynamic tool bits and a bending moment and vibration loading structure. The working conditions of two tool rests are detected simultaneously by one set of image detection mechanism, and the device has a high degree of integration and automation.