The invention discloses a composite material for repairation and maintenance of cement mortar or concrete and an application method thereof, and belongs to the technical field of building materials. The composite material comprises the following raw materials: sodium silicate, malic acid, tartaric acid, laureth-9, sodium tripolyphosphate, potassium trimethylsilanolate, ethanediol, sodium sulfate and potassium hydroxide; the preparation method comprises the following steps: mixing and stirring the raw materials in a stirring machine for 30 minutes or above, sub-packaging and sealing for storage; the application method comprises the steps of cleaning the surface of cement mortar or concrete, spraying water for wetting, and coating the surface of cement mortar or concrete with the nano-composite material for repairation and maintenance of cement mortar or concrete. The composite material can deeply permeate into the inner part of concrete, so that moisture in concrete is effectively retained, the compactness degree of concrete is improved, cracks are prevented from being produced, old and new cracks with the width of 0.3 mm or below can be repaired, erosion to concrete due to external moisture and harmful ions is reduced, and the durability of concrete is improved; besides, the composite material has the characteristics of being convenient in construction, safe, nontoxic and suitable for large-scale popularization and application, and having remarkable economic benefits and social benefits.