MOF-74 family is unstable in humid environment because its coordination bond between metal ions and oxygen atoms is relatively weak. This limits the practical application of MOF-74 material. Therefore, improving the water vapor/water stability of MOF-74 is crucial for their use in practical applications. In this work, we propose a strategy involving a trace polymer in-situ modified MOF-74. During the in-situ synthesis, polyvinylamineacid (PCH) was introduced into the structure of MOF-74 (PCH-MOF-74, PMOF-74) to form a hydrophobic environment around the unsaturated metal sites to enhance water stability. After immersion in water or acid, PMOF-74 can maintain most of the original crystal structure and gas adsorption capacity. The experimental results show that the successful incorporation of PCH into MOF can effectively improve the water vapor/water stability of MOF structures, and it is also worth further improving and enhancing the structural stability of other MOF materials with metal sites.