Numerical simulation studies on 2-D dual throat nozzle (DTN) were performed on the downstream throat height H. The contents include: effects of H on the nozzle's maximum vector angle and the flow development in the nozzle's thrust cavity. The results show that: H has a significant influence on the nozzle's thrust vector angle; especially in two cases of H greater than 1 and H less than 1

the flow development in the nozzle's thrust cavity has a large difference. In all cases

it appears that the maximum vector angle could be achieved when the flow in the nozzle's thrust cavity has changed to the supersonic flow

meanwhile the sonic line at the downstream throat of the nozzle has vanished. The nozzle can achieve the maximum vector angle with a low ratio of secondary injection in the case of H greater than 1. The nozzle could be achieved maximum vector angle at larger ratio of secondary injection in the case of H less than 1

while the maximum vector angle is greater than that in the case of H greater than 1.