Symbolic sequence analysis method was applied to analyze two-phase flow measurement fluctuating signals and some issues about selecting key parameters which were used in the algorithm were discussed. Based on the above study

we gathered eighty groups differential pressure fluctuating signals of gas/liquid two-phase flow in vertical upward pipes and extracted the time irreversebility and chi-square statistics . The study indicates when the gas superficial velocity is less than 0.02 m/s

the dynamic character of bubble flow becomes complex with the gas superficial velocity increasing. When gas superficial velocity exceeds 0.02m/s

the dynamic character becomes relatively simple from bubble flow to slug flow and the dynamic character becomes more and more complex from slug flow to churn flow with the gas superficial velocity increasing. This shows that time irreversibility and chi-square statistics can reflect the evolution character of gas/liquid flow patterns

and is a supplementary tool to understand two-phase flow pattern phenomena.