Due to the dense random deployment of heterogeneous cellular networks (HetNets), the system is more seriously affected by channel estimation errors. However, there is a lack of effective secure transmission scheme in this scenario. In order to solve this problem, a transmit antenna selection strategy based on channel estimation accuracy is proposed. First, the stochastic geometric tool is used to derive the secrecy outage probability of K-tier dense HetNets. Then the influence of channel estimation accuracy on secure performance of the system is analyzed. Finally, the validity of the theoretical derivation is verified and the influence of some parameters on the security performance of the system is analyzed.