Although terahertz (THz) spectroscopy exhibits great application prospects in the fields of biomedicine and security detection, conventional sensing schemes face unavoidable limitations in the analysis of trace-amount samples. In this paper, a terahertz absorption spectrum boosting method based on the two-dimensional stretchable metagrating structures is proposed to improve the interaction between the terahertz wave and the trace-amount samples. Based on Guided-mode Resonance (GMR) effect, the local electric field in a thin-film sample can be enhanced by simultaneously varying the periodic length P of PDMS substrate and nano-Ag reflective layer, so that wideband terahertz absorption spectra can be greatly enhanced. This strategies for utilizing reflective layers exhibits a great absorption enhancement factor, of about 111 times, in a wideband terahertz frequency range, facilitating the identification of different trace-amount analytes, such as thin α-lactose films. The proposed method provides a new, to the best of our knowledge, choice for the enhancement of ultra-wide terahertz absorption spectra, and paves the way for the detection of trace-amount chemical, biomedical, or organic materials in the terahertz regime.Terahertz absorption spectroscopy enables many new potential applications, and demonstrates great promise in molecular fingerprint detection. THz detection is nondestructive, and many complex molecules have feature absorption resonance peaks in the THz spectral frequency range; according to molecular rotational and vibrational modes. However, traditional detection modes for identifying the fingerprint spectrum of trace-amount samples usually use more sample materials because of the diffraction of the THz. The response between waves and matter is also very weak. In order to improve the detection capability of trace-amount analytes, an effective strengthening strategy is to introduce additional resonance micro-structures to enhance the interaction between waves and matter. In this study, we introduce a two-dimensional stretchable metagrating periodic structures with reflection mode by numerical simulation. Compared with other methods, the proposed scheme provides three main advantages, as follows: 1) a great broadband trace-mount terahertz absorption enhancement factor can be realized based on reflection mode supported by nano-Ag reflective layer, providing the advantages of simple design, only the reflection spectra needs to be measured, greatly reducing the workload, and easy adjustment of the absorption enhancement range; 2) the enhanced absorption spectra can be built by connecting a series of resonant peaks of fixed incident terahertz waves obtained by changing the stretch factor S; 3) absorption enhancement factors of about 111 times can be achieved numerically in an ultra-broadband terahertz band for 0.2 μm thick lactose analytes, enabling the explicit identification of various analytes, such as trace-amount thin film samples.Firstly, the structural schematic the numerical analysis method, the principle of generating resonance peaks, and the problem of stretching substrate deformation are given in succession in section 1. In the second part, the enhancement factors based on the GMR model generation, Lorentzian model of lactose, and the electric field distributions of metagrating structure at the x-y plane around 0.53 THz with and without the thick lactose are illustrated in order. Finally, we get the optimal values by systematically scanning various parameters, including the thickness t of the lactose film (ranging from 0.2 to 1.0 μm in a step of 0.2 μm), the thickness h₁of the PE bar (ranging from 55 to 95 μm in a step of 10 μm), and the width of the PE bar (ranging from 140 to 180 μm in a step of 10 μm). The optimal conditions considered are: coated lactose thicknesses t=0.2 μm, PE bar thickness h₁=55 μm, and PE bar width W=180 μm. The proposed absorption enhancement strategy for thin samples is relatively easy to manufacture and measure, which paves a new way for future high-performance terahertz fingerprint detection with two-dimensional stretchable metagrating structures.