The intra-aorta pump is a novel left ventricular assist device (LVAD) that assists the heart without the need for percutaneous wires and conduits. It is implanted between the radix aortae and the aortic arch to avoid damage to the aortic valve. To predict the mean pressure head and blood flow, a nonlinear lumped parameter model, which does not need the parameters of the circulatory system, is established. The model includes a speed-controlled current source, an internal resistor, and an inductance for simulating the pressure–flow rate relationship. The speed-controlled current source is used to represent the blood flow caused by the kinetic energy from the impeller, the internal resistor is used to stimulate the resistance character of the radial clearance of the intraaorta pump, and the inductance is used to model the inertia of the blood that passes through the radial clearance. Each part of the model has clear physical significance, which is helpful for extending the model to other blood pumps. It can generate all status of the pump from suction to pulmonary congestion. The model is summarized as a function of the pressure head, the blood flow, and rotational speed of which the values of parameters in the model are determined by experiment. The model and prediction method are tested experimentally on an in vitro mock loop. A comparison of the predicted pressure head obtained from our model with experimental data shows that our model can predict the differential pressure accurately with error <5% for all experimental conditions over the entire range of intended use of the intra-aorta pump.