Disclosed are a true triaxial experimental device and method capable of obtaining the after-peak curve and residual strength of brittle rock. According to the device, a rigid load application framework is arranged in the middle of a fixed high-rigidity counter-force framework, and large principal stress load application actuators indirectly apply loads to a rock sample in a pressure chamber through the rigid load application framework. The method comprises the steps of preparing and sealing the rock sample, and mounting a displacement sensor; mounting the sample, and accurately centering and clamping the sample in a displacement control manner to eliminate gaps; finely adjusting the displacement sensor to a a measuring range; sealing the pressure chamber, and filling the pressure chamber with hydraulic oil; synchronously applying minimum, intermediate and maximum principal stresses, applying axial loads to the rigid load application framework by the first and second maximum principal stress load application actuators, applying the maximum principal stress to the sample through the micro-deformation of the rigid load application framework, and simultaneously measuring the deformation of the sample; applying loads to the sample to make the sample enter an after-peak deformation stage and damaged; continuing applying loads to the sample until the residual strength is obtained; sequentially removing the maximum, intermediate and minimum principal stresses, disassembling the damaged rock sample, and saving experimental data.