BP artificial neural network was applied in the research of identifying dynamic force of hydro-pneumatic suspension. A dynamic model of 1/4 vehicle with hydro-pneumatic suspension was built and a neural network was established based on this suspension model. Dynamic force of hydro-pneumatic suspension was identified by input and output data of hydro-pneumatic suspension. Identifying results of neural network and equivalent linearity were compared. Identifying results of neural network are better than equivalent linearity. It provided a new method for calculation, designing and active controlling of hydro-pneumatic suspension.