Time‐delay dynamic systems are widely existed in industrial applications owing to the measure, control or other processes. To carry out system analysis, control and fault diagnosis, the identification of time‐delay systems becomes more and more important. This article considers the identification of time‐delay ARX models based on a novel two‐stage algorithm. Firstly, a 2‐copula criterion based time‐delay estimation method is presented by using a measure of dependence between the model input and output. This method can obtain the time delay without the estimates of the parameters. Secondly, a multi‐gradient algorithm with adaptive stacking length is studied. This algorithm accelerates traditional stochastic gradient algorithm by taking several recent gradients in each iteration. The stacking length, that is, the number of the gradient used in a step, is determined by the Armijo criterion. The proposed algorithm is validated by numerical experiments and the modeling of unmanned aerial vehicle data.