Abstract: Aiming at the key technical problems in the engineering application of Static Cracking Agent (SCA), such as random crack propagation, low energy utilization efficiency, and susceptibility to ejection, a “directional energy-concentrating structure” integrating directional guidance, energy concentration, and ejection control was designed. This structure consists of three components: a directional slit tube, an elastic woven bag, and quick-connect plugs. Through physical constraint and structural guidance, it aims to achieve directional concentration of SCA expansion force and convert axial ejection force into radial expansion. To systematically reveal its mechanism, based on the analysis of the expansion mechanism of SCA hydration reaction, an evolution model of SCA expansion stress under constrained structure was established. Four key parameters were defined: maximum expansion stress (P_max), equivalent acceleration coefficient (k), peak time (t_p), and post-peak pressure decay coefficient (c). This clarifies the internal mechanism by which the directional energy-concentrating structure regulates SCA expansion behavior through energy accumulation and stress guidance. Subsequently, three sets of comparative tests were designed using the external steel tube method, including conventional pouring, directional constraint, and directional energy-concentrating constraint. Resistance strain gauges and K-type thermocouples installed on the steel tube wall were used to collect strain and temperature data in real-time during the SCA reaction, recording the evolution of its expansive mechanical properties. The experimental results show that the expansion stress evolution of SCA under allconstrained structure exhibits a three-stage characteristic of “slow growth – rapid growth – post-peak decline”, but the directional energy-concentrating constraint demonstrates significant performance improvement. Taking the test condition with a ϕ50 mm steel tube as an example, in the directional energy-concentrating constraint test, the peak expansion stress in the preset slit direction reached 162 MPa, the reaction time was shortened to 20 min, and the peak temperature rose to 238 °C. Compared with conventional pouring and directional constrained structure, the peak expansion stress measured at the slit locations by the directional energy-concentrating structure increased by 57.50%−79.12% and 58.80%−76.45%, respectively. Its maximum expansion stress growth rate reached 8.22 MPa/min, significantly higher than the 3.67 MPa/min and 3.92 MPa/min of the control groups. The peak temperature increase rates were 87.84% and 133.90%, respectively. Energy utilization calculations indicate that this structure nearly doubled the energy conversion efficiency of the SCA hydration reaction compared to the conventional pouring method. Meanwhile, fitting the experimental data with the established model yielded a goodness-of-fit higher than 0.90. Its key parameters (P_max, k) followed the pattern of "directional energy-concentrating constraint > directional constraint > conventional pouring", while (t_p, c) followed "conventional pouring > directional constraint > directional energy-concentrating constraint," consistent with the theoretical analysis. This verifies the reliability of the model and the regulatory effect of the directional energy-concentrating structure. The mechanism of SCA hydration and expansion under directional energy-concentrating action lies in: the quick-connect plugs achieving axial sealing, suppressing ejection, and promoting the conversion of axial force to radial expansion; the directional slit tube guiding high concentration of expansion stress in the preset direction; and the overall sealed structure facilitating the accumulation of reaction energy and high-temperature, high-pressure steam.