A stratospheric airship with multiple actuators requires control allocation algorithm to meet the requirements of path following while respecting system constrains. This paper proposes a constrained control allocation method for the stratospheric airship on the basis of vector field path following controller. The control system is divided into two levels, path following and control allocation. Firstly, the high level controller is designed to generate the virtual control inputs to low lever controller. Secondly, the constrained control allocation is proposed to distribute the control command to every actuator. The constrained control allocation can be transformed into a convex quadratic programming problem which can be solved by a recurrent neural network. Finally, several simulations are given to prove the effectiveness of the control system.