The invention discloses a method for simulating offshore oilfield micro fracturing injection increase crack propagation on the basis of fluid-solid-heat coupling theory. The method comprises the following steps that geological characteristic parameters are obtained on the basis of offshore micro fracturing well geological data; a hydraulic crack propagation model is built, and fluid pressure and filter loss in a crack are obtained; on the basis of a reservoir matrix model, dynamically changing pore pressure in a reservoir is worked out; on the basis of elastic mechanics and permeation fluid mechanics, a pore elastic deformation relation between fluid and rock is built, that is to say, a fluid-solid coupling model is built, and by means of the calculated pore pressure, rock strain caused bythe fluid can be obtained; a heat effect relation between the temperature and the rock is built, a strain, porosity, permeability and temperature fluid-solid-heat coupling model is built, the permeability and porosity after coupling change are obtained, the pore pressure after three-field coupling change is obtained, the changed pore pressure reacts on a Darcy filtration model, and the crack extension dynamic of the next moment is obtained. According to construction and geological parameters, the dynamic extension situation of the hydraulic crack and real-time change situation of the reservoir parameters in the offshore micro fracturing well long-term injection increase process can be predicted according to the construction and geological parameters.