Data accuracy is an important index of the shipborne IRST, and the installation error is an influence factor of the data accuracy. According to the working principle of IRST, the errors of installation on board were analyzed, five coordinate systems were established. Through the matrix transformation, the calculation method the installation error of the effect on accuracy was derived. The errors caused to various working conditions were calculated. The results show that the installation error has a great influence on the IRST, and it is easy to lead to the data accuracy deviation when the vertical and horizontal shaking is too large so it is necessary to control or compensate for it.