We investigate herein the scale effect and anisotropy of jointed rock mass (JRM) from the perspective of acoustic emission (AE) characteristics and estimate the size of the representative element volume (REV). First, we propose an AE calculation based on the discrete element method (DEM) and use the statistical results of joint planes to generate a discrete fracture network. Next, we calibrate the micro-parameters of the rock matrix and the joint plane based on physical experiment and the single plane of weakness theory, respectively. Finally, we use the proposed model to numerically simulate the AE characteristics of a JRM and estimate the size of the REV. The use of different model sizes and layer orientations shows that the AE event magnitude follows a power-law distribution. The frequency of AE events with different magnitudes follows a normal distribution, and a negative exponential relationship is found between the frequency of AE events and the number of cracks associated with each AE event. When the model size exceeds 10 × 10 m, the parameters of AE events (accumulated frequency, magnitude, frequency of AE events associated with only one crack, frequency of AE events associated with over ten cracks, and maximum crack number associated with each AE event) remain essentially constant. This means that the size of the REV is 10 × 10 m. The proposed model should also prove useful for further research into the fracture mechanism of JRM.