This paper analyzes security region with artificial noise (AN) based on secrecy outage probability under the assumption that the eavesdropper's channel state information and location are unknown to the transceiver. By utilizing beamforming, the legitimate receiver transmits the AN in the direction of the legitimate transmitter to impair the eavesdropper more effectively. Based on it, a closed-form secrecy outage probability expression is derived to define the security region. Furthermore, a concept called safe transmission interval is proposed to measure the secrecy performance. Simulation results are in good agreement with the theoretical expression and show the impacts of transmit antenna number, target rate and power allocation on the security region.