Aiming for the features of Digital Phosphor Oscilloscope(DPO) 4 000 series，C/C++ language is adopted to program and design oscilloscope application class. Then based on the analysis of some certain project，an application class suitable to this kind of oscilloscope is designed. The class methods mainly include oscilloscope resources search，oscilloscope opened and closed, set and read oscilloscope data back etc. The design is proved to be feasible and applicable by the experimental results.