The invention discloses an uncertainty evaluation device and method of an indirect full-optical path spectrum detection system. The uncertainty evaluation device includes a constant temperature oil tank, an optical fiber pressure detection system, a computer, a high-precision platinum resistor and a grating sensor. The evaluation method comprises the following steps that: test data are obtained; a measurement model is established; the uncertainty of the work straight line of the grating sensor is evaluated; and the uncertainty of the optical fiber pressure detection system is evaluated. According to the uncertainty evaluation device and method of the indirect full-optical path spectrum detection system of the invention, the grating sensor is adopted; uncertainty evaluation is performed on the measurement accuracy of picometer-level wavelength shift quantity of a non-removable wavelength modulation type optical fiber pressure detection system through adopting an indirect method; an uncertainty analysis experimental system is designed and constructed; system error sources are analyzed; a theoretical measurement model and an uncertainty analysis method are established; and the uncertainty value of system measurement errors can be obtained.