The stimuli-responsive DNA hydrogel has attracted wide attention in the fields of chemical and biological sensing. However, it is still a challenge to integrate characteristics with low-cost, high mechanical strength, and signal self-expression into a DNA hydrogel simultaneously. Herein, a stimuli-responsive 2D photonic crystal double network DNA hydrogel (2D PhC DN-DNA hydrogel) sensing platform is developed via combining the signal self-expression of 2D PhC array with the selective recognition of polyacrylamide (PAM)/DNA DN hydrogel. The change of DNA configuration induced by specific target triggers the change of 2D PhC DN-DNA hydrogel volume, leading to a shift of the Debye diffraction ring diameter. In order to verify the feasibility of this strategy, the 2D PhC DN-DNA hydrogel with C-rich sequences is chosen as a proof-of-concept. The results indicate that the hydrogel has good detection performance for pH and Ag+/Cys. And the Debye diffraction ring diameter of the hydrogel is correlated with the concentration of the Ag+/Cys in the range of 0.5-20 μM. Compared with previously pure DNA hydrogel sensing platform, the 2D PhC DN-DNA hydrogel features low-cost preparation process and label-free determination. Meanwhile, only a laser pointer and a ruler are needed for the determination of targets, which shows that the hydrogel has application prospect in the development of portable response equipment.