Abstract: In the manufacture and application of the complicated controlling, launching, tracking systems, the angular error caused by the deviation of mounting position of subsystems or assemblies in a whole system will influence the controlling, tracking and launching accuracy or other measurement results, so the error must be measured and corrected. It is very important to control the position error.A new method for measuring the boresight error between optical axes based on facular center located with vision image is presented. A machine vision angle metering system based on LABVIEW ( a virtual instrument platform ) was also constructed. It was used to align some axes (e.g.axis of launch, axis of targeting, axis of laser designator, etc.) in a large weapon system, and a satisfactory test result was got.