Newhall navel oranges exhibiting various degrees of maturities were selected as the research object. A sophisticated technique, involving headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry, was employed to meticulously analyze the key flavor-active substances in the pulp and to track the evolving trends of these compounds at different maturities. This research revealed that the a total of 19 aroma compounds were detected in the pulp of Newhall navel oranges at 3 different maturities, including pre-mature, mature, and post-mature. The types of aroma compounds in the pulp of Newhall navel oranges showed no significant differences across various maturities. However, their concentrations exhibited notable fluctuations with changes in maturity. The terpenoids were the main aroma compounds in the pulp of Newhall navel oranges. Specifically, the concentrations of hexan-1-ol, octan-1-ol, geranial, and damascenone displayed an ascending trend from the pre-mature to the mature stage, followed by a decline from the mature to the post-mature stage, peaking during the mature stage. The contents of remaining compounds exhibited a gradual increase across three distinct maturity levels, with their concentrations peaking in the post-mature stage. The odor activity value (OAV) method was used to analyze the flavor-active substances in Newhall navel oranges. It was found that among the compounds with OAV>1, the OAV values ranked in descending order as follows, D-limonene, hexan-1-ol, damascenone, octanal-1-ol, linalool, carvone, neral, geranial, citronellol, and L-perilla aldehyde. Through aroma profile radar chart analysis, it was determined that the pulp of Newhall navel oranges was primarily characterized by citrus and fruity aromas, accompanied by prominent grassy, floral, and sweet aromas, along with minimal woody and unpleasant odors. The citrus and fruity aromas were most pronounced at the post-mature stage. This research was expected to provide an experimental foundation for further studies and development of Newhall navel orange pulp.