In future 20 years or even longer

the L-band digital aeronautical communication system（L-DACS）is needed for aeronautical communication.In order to separate useful signal in the receiver

by studing EASI algorithm and variable step-size EASI algorithm.Kurtosis variable step-size EASI algorithm based on optimal estimation function is proposed.According to the relationship between the covariance of kurtosis and the state of separation

step-size is controlled with the covariance of kurtosis

it overcomes the contradiction inherent in existing approaches between convergence speed and steady-state error.Meanwhile

two different estimation functions are used in different state of separation.It decreases the steady-state error efficiently.The simulation experiment results show that the proposed algorithm has been greatly improved in convergence speed and stability compared with conventional algorithms.