At present GPS is applied to various situations because of its confidence and usefulness. Position calculated by GPS makes some errors caused from many different factors which GPS signals made. The greatest error factor which affects the accuracy and the precision of positioning by GPS is lack of the number of satellites you can see in the sky. To reduce this error factor and to improve the precision and accuracy of GPS positioning many projects are carried out research, such as QZSS, pseudolite system. These systems have potentiality to make the precision of GPS positioning under worse situation that you can see few GPS satellites because they increase the number of satellites which are available to use for position calculating. However, they require much time and expensive device for their infrastructure. We paid attention to GPS calculating method itself. We adapted Kalman filter to GPS positioning calculation. We improved the precision and accuracy of SPS positioning in stand-alone mode under worse situation adapted the Kalman filter parameter.