The experimental study of the Raman spectral character for liquid isooctane(2,2,4-trimethylpentane, ATM) was conducted by moissanite anvil cell at the pressure of 0～1.2 GPa and the ambient temperature. The results show that the Raman peaks of the C—H stretching vibration shift to higher frenquencies with increasing pressures. The relations between the system pressure and peaks positions is given as following: ν2 873=0.002 8P+2 873.3; ν2 905=0.004 8P+2 905.4; ν2 935=0.002 7P+2 935.0; ν2 960=0.012P+2 960.9. The Raman spectra of isooctane abruptly changed at the pressure about 1.0 GPa and the liquid-solid phase transition was observed by microscope. With the freezing pressure at ambient temperature and the melting temperature available at 1 atm, the authors got the liquid-solid phase diagram of isooctane. According to Clapeyron equation, the authors obtained the differences of volume and entropy for the liquid-solid phase transition of isooctane: ΔVm=4.46×10-6 m3·mol-1 and ΔS=-30.32 J·K-1·mol-1.