A portable test system was designed in order to investigate the relationship between the Single-Event-Upset (SEU) affairs of SRAM-based FPGAs and the dose of high-energy particle in low-altitude environment.By using the test system, SEU tests of SRAM-based FPGAs were conducted at six different altitude sites in a certain area.The average elevation of the area is from 3000 m to 5000 m, which is appropriate for simulation of low-altitude flight environment.In the tests, the system gained lots of field data, which was then analyzed by using Matlab.According to the test result, the scientificity and practicability of this test system were verified and analyzed from such aspects as the storage structure of the SRAM-based FPGA, the SEU generating mechanism, and the working principle of the test system.The analysis result shows that the portable test system is effective, which can serve as a reference for the selection and application of SRAM-based FPGAs in the aerospace field.