Spontaneous imbibition (SI) is an important method to improve oil recovery in tight sandstone reservoirs. Commonly, the physical simulation of SI is performed at atmospheric pressure but the characteristics of spontaneous imbibition under confining pressure (SIUCP) is often neglected. In this study, oil distribution in tight cores was obtained in combination of high pressure mercury intrusion (HPMI) measurements and low-field nuclear magnetic (LF-NMR) measurements. After that, oil recovery for SI and SIUCP of tight core samples with all faces open (AFO) were obtained using LF-NMR measurements. Finally, a new scaling law for SIUCP was proposed to predict shut-in time in field scale. The results showed that 95.94–98.12 wt % of the oil was distributed in nanopores (0.1 ms < T2 < 100 ms) of core samples, and the average amount of oil in nanomicro-pores, nanomeso-pores and nanomacro-pores were 34.04, 40.15, and 22.75 wt %, respectively. Ultimate oil recovery for core samples were 22.41, 44.41, 57.27, 61.84, an...