Abstract: The lunar pole's water ice is essential for understanding the moon's evolution and building future lunar research centers. However, present remote sensing methods and samples cannot accurately determine its appearance, composition, and origin. The Chang'e-7 (CE-7) mini-flying probe will carry the LUnar soil Water molecule Analyser (LUWA) to discover water ice at the permanently shadowed region for the first time. This paper describes the compositional structure of LUWA and the comprehensive detection approach, comprising drilling, sampling, sealing, heating and analysis. A ground calibration testing methodology and calibration framework for three functional modules dedicated to water measurement were developed to ensure the high sensitivity and wide dynamic range of water content detection and precise analysis of water isotopes in orbit. In parallel, a lunar in-situ exploration test platform replicated drilling, sampling, sealing, heating, and analysing lunar simulant regolith, validated the payload's performance metrics, and provided critical support for water ice content data assessment in lunar soil.