Abstract: Recently we carried out SEU measurements of some devices in a heavy ion accelerator. Because the ions with higher LET values don't have larger ranges in Silicon, when they are used to probe a device with thick die layer, they are either not able to reach the sensitive volume, or deposit very limited energy in the sensitive volume even though they reach there, as a result, the measured σ-LET curve greatly deviates from weibull function. These kinds of data are usually regarded as unsatisfactory and discarded. In fact, these data may contain very important physical information, and if processed properly, can provide some key parameters about the sensitive volume. To introduce the suggested data processing method, the SEU data for IDT7164 is processed as an example, from which such key parameters as the die layer thickness, the sensitive volume thickness, as well as the threshold of deposited energy for upset are extracted, which are well in agreement with abroad measured results. These parameters are not only very important for SEU sensitivity evaluation of onboard devices, but also difficult to acquire through other experimental methods. Finally, based on the introduced method, some preliminary thoughts are put forward about how to use combination of ions with large and short ranges to probe the key parameters about sensitive volume of a device. Furthermore, how to select proper combination of ions according to the characteristics of different domestic accelerators is discussed.