Exactly measuring the raw speed is sti1l one of the most important tasks in trajectory measuring. Modern Dopplar radar is of practical use，but there are many weak points in processsing practical datum. This paper uses modern statistical method，called "Robust estimation"，to calculate the first speed，the precision of which can be estimated，even in the worst condition by improving the data processing in the raw speed measuring radar. With the same method，the coefficient of resistance can also be determined. The experiments have heen proved to be of these correct conclusions.