The invention provides a determination method for an Ostwald coefficient of oil dissolved gas in FR3 vegetable insulating oil. The determination method comprises the following steps: preparing mixed standard gas according to requirements; preparing a blank oil sample of the FR3 vegetable insulating oil; preparing a sample oil sample of the FR3 vegetable insulating oil; carrying out first-time oscillation balance at 50 DEG C and extracting oscillation balance gas; carrying out second-time oscillation balance at 50 DEG C and extracting oscillation balance gas; accurately recording a degassing volume; carrying out gas chromatographic analysis; calculating each component of the dissolved gas in sample oil; calculating to obtain the 50 DEG C Ostwald coefficient Ki of the FR3 vegetable insulating oil. By adopting the determination method provided by the invention, the Ostwald coefficient of the oil dissolved gas in the FR3 vegetable insulating oil at 50 DEG C can be accurately detected and obtained, so that the content of each component of the dissolved gas in the FR3 vegetable insulating oil is accurately and quantitatively calculated.