Summary: We analyze the quantum Fisher information (QFI) for a particle detector coupled to a thermal electromagnetic field in the cosmic string spacetime. It is found that vacuum fluctuation, temperature, detector polarization and nontrivial spacetime topology affect the QFI. Vacuum fluctuation and temperature degrade QFI. When deficit angle parameter \(\nu = 1\) and detector is far away from the string, the results in free Minkowski spacetime are restored. When detector is close to the string, QFI can be effectively enhanced; specially when detector lies in the string and is not polarized along axial direction, the detector seems like a closed system, and QFI completely is not affected by the thermal electromagnetic fluctuation. For nonzero detector-string distance, QFI appears oscillatory behaviors as detector-string distance varies. In addition, this detector eventually evolves to a thermal state, which is not related to the initial state and other various parameters, which implies QFI cannot persist in for long evolution time in the cosmic string spacetime. In principle, the detector polarization, detector-string distance, temperature and deficit angle parameter provide us with more parameters to steer the QFI behaviors, which might be helpful to enhance the precision of sensing the characters of cosmic string spacetime.