Based on pair potential of atoms determined by general nonlocal model pseudopotential and molecular dynamics simulation techniques of NPT ensemble, we investigated micrody-namical behaviors of supercooled liquid Mg-Ca alloy, examined characteristics of atomic autocorrelation functions of density with time、 wavevector and temperature. Results show that, with deseasing temperature, correlation length of autocorrelation function increases. In the supercooling range, the system exhibits structure slowing down phenomenon to some extent. In addition, results of model coupling theory, within the supercooling range in the present paper, are applicalle to liquid Mg-Ca alloy.