The invention belongs to the technical field of sensors, and provides a composite insulating layer for a thin film sensor and a manufacturing method of the composite insulating layer. The composite insulating layer and the manufacturing method are used for solving the problem that in the prior art, as thermal expansion coefficients of an insulating layer and a sensitive functional layer are mismatched, the high-temperature adhesive force of the functional layer is poor. The composite insulating layer is composed of a heat growth Al2O3 layer and a SiAlO ingredient gradient layer which are sequentially stacked from bottom to top; and in the thin film growing direction, the silica contents in ingredients in the SiAlO ingredient gradient layer are gradually increased, and meanwhile, the aluminum contents in the ingredients in the SiAlO ingredient gradient layer are gradually decreased. The thermal expansion coefficient of the composite gradient insulating layer can be gradually changed along with gradual changes of the ingredients, the requirement for matching with the thermal expansion coefficients of different sensitive functional layers is met, thermal stress generated by mismatching of the thermal expansion coefficients of the insulating layer and the sensitive functional layer is reduced, and the adhesive force of the thin film sensor is improved; under the high temperature condition, the reliability and the stability of the thin film sensor can be effectively guaranteed, the efficiency losing rate of devices is reduced, and the service life of the thin film sensor is prolonged.