The invention provides a determination method for the original water saturation of a tight sandstone reservoir. The method comprises the steps of obtaining a sampling size and a target echo interval; performing sampling according to the sampling size, and obtaining a target test sample; performing nuclear magnetic resonance processing on the target test sample according to the target echo interval so as to obtain the original liquid fluid saturation of the target test sample; performing distillation and extraction on the target test sample so as to obtain the original oil saturation of the target test sample; accurately obtaining the original water saturation of the target test sample according to the original liquid fluid saturation and the original oil saturation. Due to the fact that the target test sample can best reflect the status of the tight sandstone reservoir, the original water saturation of the target test sample is the original water saturation of the tight sandstone reservoir, the purpose of accurately determining the original water saturation of the tight sandstone reservoir is achieved, and the basis is provided for oil and gas reservoir evaluation and the like.