In pressure distribution measurement of free-flight objects using Pressure-Sensitive Paint (PSP), it is difficult to obtain the reference image corresponding to the signal image. Therefore, we are developing a pressure measurement technique using the intensity-based method with a monochrome camera. In this paper, we call this method the mono-luminophore method. In this method, the reference images at various attitudes are acquired before a free-flight test, and the reference image at the attitude closest to the signal image is used for pressure calculation. However, it could not cope with the spatial variation of the excitation light, and the effect of the spatial variation appeared in the pressure distribution. In this paper, a pseudo-reference image, which considers the spatial variation of the excitation light, is created by using simulation. Comparing the pressure coefficient distribution obtained by the proposed method with that obtained by the conventional method, we succeeded in improving the accuracy of alignment and suppressing the influence of the spatial variation of the excitation light. Furthermore, the photodegradation of the PSP was also limited to 5% by suppressing the number of pre-acquired reference images.