Using unmanned aerial vehicles （UAV） is an effective means to solve firefighting problems in urban high-rise buildings. This paper proposes a control strategy based on constraint following theory for the pan/tilt water-jet nozzle tracking to solve the problem of UAV pan/tilt movement control. First， according to the actual firefighting demand in high-rise buildings， the two-degree-of-freedom driving structure of the pan/tilt water-jet nozzle is designed. Second， Denavit-Hartenberg （D-H） method is used to model the pan/tilt system， and the pan/tilt kinematics equation is established. Then the dynamic model of pan/tilt without constraints is constructed according to the Lagrangian equation. The expected trajectory of the pan/tilt water-jet nozzle is regarded as the constraint. Without introducing any variables or pseudo-variables such as the Lagrange multiplier， the analytical formula of driving torque which can meet the requirement of constraints following is obtained based on the Udwadia-Kalaba equation， and continuous state feedback control is realized， which achieves the purpose of water-jet nozzle trajectory tracking. What’s more， to reduce the tracking error， the Baumgarte method is used for stability processing， and the trajectory tracking control is simulated in Matlab/Simulink environment. Finally， an experiment platform with the digital signal processor （DSP） as a control core is built to conduct the trajectory tracking control. The results show that the control algorithm based on constraint following theory could effectively complete the tracking task and achieve high-precision tracking of the desired trajectory.