Continental shale reservoirs are characterized by an abundant number of nanoscale pores, rendering it challenging to describe the phase transitions of fluids in nanopores through conventional PVT tests. The unconventional phase behavior observed within these nanopores directly impacts fluid components and mobility, thereby influencing shale oil production. This study addresses this challenge by establishing an experimental platform capable of precisely characterizing phase changes within shale nanopores. Through the development of an innovative experimental method, we visualize the phase behavior of nanoscale fluids under high-temperature and high-pressure conditions. Several nanofluidic chips with pore sizes ranging from 30 nm to 1000 nm were meticulously designed and fabricated to facilitate nanoscale fluid experiments. By quantifying the effect of nanoconfinement on fluid phase behavior, particularly by observing and recording the bubble point pressures of pentane and hexane within nanopores of varying sizes, several key findings were drawn. The experimental results underscore that both pentane and hexane exhibit decreased bubble point pressures as pore size decreases. Notably, the decrease trend amplifies with diminishing pore size, with the confinement effect becoming apparent at the 100 nm threshold. Beyond this point, the alteration in bubble point pressure becomes negligible. If the pore size is below 100 nm, the variation of bubble point pressure is significantly intensified. For the 30 nm pore chip scenarios, the bubbles initially manifest at the entrance of the nanopore channel, followed by a progressive gasification process. As the gas column advances, adsorption phase fluid is observed on the pore wall. Gasification occurs preferentially within the porous media channel at locations where the capillary forces are weak. The findings of this study will provide empirical evidence and improvement direction for future research on the fluid phase theory under the influence of nanopore confinement effect.