Based on the idea of rapid prototype, a set of aftertreatment OBD system for light duty gasoline vehicle that conformed to China Ⅵ emission legislation was developed. The system hardware was customized based on NI PXI platform, which could communicate and collect engine operating parameters and sensing signals ofthe aftertreatment system including three-way catalytic converter（TWC）and gasoline particulate filter (GPF). A neural network-based fault diagnostic model and a state machine-based fault decision model were developed with MATLAB /Simulink which were then compiled into codes and downloaded to the real-time controller. The configuration of system definition file and the design of interactive interface were conducted with VeriStand software in the host computer and the real-time monitoring of system status was finally realized. In the end, the aftertreatment OBD system was verified by the bench test and the drum test. The results show that the developed system can diagnose the aftertreatment components smoothly in the bench steady-state condition and the real vehicle driving cycle and make reasonable fault decisions.