Abstract: Aiming at the limitation of traditional artificial noise constrained by channel degrees of freedom, this paper investigates the physical layer security performance of pilot-based codebook artificial noise (PCAN) in MIMO systems. Instantaneous channel state information (CSI) of eavesdroppers is unavailable to legitimate communication parties, hindering accurate assessment of physical layer security rate for MIMO systems. This paper formulates the statistical model of eavesdropper channels under the maximum entropy principle, and takes secrecy outage probability (SOP) to measure the security performance of MIMO systems. The upper bound of eavesdropping signal-to-noise ratio is derived to follow the beta-prime distribution, and SOP is expressed as the regularized incomplete beta function. Simulation results indicate that secure transmission performance of MIMO systems can be improved by adopting the PCAN scheme under unknown eavesdropping CSI conditions.