The present paper investigates the Raman spectral character of liquid 2-methylpentane by an experiment at the pressure of 0-1.5 GPa and the temperature of 26 degrees C, and defines the relation between the pressure and the Raman peak of 2-methylpentane at ambient temperature. The result shows that there are five characteristic Raman peaks in 2-methylpentane defined as v (CH2) and v(CH3), and all of them move to high position as the system pressure increases. The relation between the system pressure and peaks positions is given as following: v(as), (CH3) = 0.013 1p + 2 960.1, v(s), (CH3) = 0.008 8p + 2 871.0, v(as) (CH2) = 0.008 9p + 2 930.2, v(as) (CH2), = 0.007 0p + 2 903 and v(s) (CH2) = 0.007 9p - 2 844.7. On the other hand, 2-methylpentane is reliable as a liquid pressure gauge for high pressure experiment. The equation applied to demarcate system pressure is also showed: p (MPa) = 76.2 (deltav(p))2 960 + 21.65(r2 = 0.995 8). This is probably the first organic liquid gauge, especially for systems not expected to emergence of Si, Al and hydroxyl matter.