Abstract: In the positioning and altitude determination system,the tight GPS/INS coupling and loose GPS/INS coupling both have advantages and disadvantages.The loose coupling has good reliabilities but low precision while the tight coupling has high precision but poor reliabilities.Hence,it is desirable to design a Kalman filter,which offers not only high precision but also good reliabilities.Based on the consistent INS error state equation,a multiplex filter is proposed with two different observation equations of loose coupling and tight coupling.In the multiplex filter,the different solutions can dynamically be adopted according to actual GPS observations.in order to ensure both the accuracies and reliabilities.To verify the effects of the multiplex filter,actual data is processed respectively with three coupling modes.From the analysis and comparison of the processing results,we can found that there are obvious advantages of dynamic coupling using the multiplex Kalman filter both on the accuracies and the reliabilities,comparing with both loose coupling and tight coupling.