The internal filling conditions and long-term reinforcement effects of grouting in earthen site cracks are difficult to be accurately identified, and the absence of systematic non-destructive evaluation methods has constrained scientific and refined conservation of such heritage sites. This study was conducted through on-site tests in both arid and humid environments, and the applicability of various non-destructive techniques, including ultrasonic wave velocity, infrared thermography, ground penetrating radar (GPR), color difference, and high-density resistivity, was systematically compared for evaluating the effectiveness of crack grouting. The research design included comparative tests conducted before and after grouting on typical cracks at the Suoyang City site, as well as the detection of several previously grouted cracks at both the Suoyang City and Jinsha sites. Results demonstrate that crack filling and structural continuity can be effectively identified by wave velocity and GPR, with post-grouting being characterized by increased wave velocity and weakened radar reflections. High-density resistivity imaging was shown to reflect slurry infiltration pathways and resistivity changes, with localized resistivity decreases observed after grouting and subsequent recovery occurring during the curing process. Infrared thermography and colorimetry were found to provide rapid and intuitive information on surface moisture and material compatibility, but were easily affected by environmental factors, such as light, temperature, and surface roughness. Moreover, signal responses were found to exhibit significant differences between arid and humid sites, indicating that cross-environment field testing is an important prerequisite for establishing identification rules for crack grouting evaluation, and evaluation results should be interpreted in conjunction with environmental and site-specific conditions. Based on complementary multi-method analyses, a comprehensive whole-process on-site evaluation procedure for crack grouting in earthen sites was proposed, covering pre-grouting surveys, documentation of the grouting process, and post-curing integrated assessments. The findings provide cross-environment empirical evidence and methodological references for the non-destructive evaluation of grouting in earthen sites and facilitate the establishment of standardized and systematic on-site evaluation frameworks.