A novel substrate-free acrylamide photopolymer was proposed to improve holographic sensing characterization. The diffraction spectrum response of reflection volume grating recorded in the medium was characterized for exploring the improvement of sensitivity. The compared result indicated that the response rate and sensitivity were evidently improved by absorption of double surface in substrate-free polymer. The thickness of the sample as a significant factor was discussed in detail experimentally. During the sensing process, the inhibition concentration and concentration constant of organic vapor were extracted to evaluate the significance of sample thickness. Simultaneously, optimization of thickness could be considered as an effective approach to improve the response rate of holographic sensing. The reversibility of a novel holographic sensor with double surface was demonstrated by recovery measurement. The swelling ratio indicated that the peak wavelength shift was attributed to the expansion of binder induced by absorption of organic vapor. Theoretically, the sensing physical mechanism and the dynamic swelling process were analyzed and simulated using a diffusional model with nonlocal response. These experimental results provide an effective strategy for improving the response of a holographic sensor and accelerate the development of the holographic optical element based on photopolymer.