The typical analytical part-load performances of constant speed single shaft small gas turbine with centrifugal compressor and its cogeneration are given.The influence of gas turbine design parameters and steam side design parameters are thoroughly investigated.The typical efficiency curve and statistical formula obtained for this type gas turbine are consistent with the practical data.The part-load performance of cogeneration is studied with saturated steam supply.It is pointed out that the approaching temperature difference may be negative in low load condition with high steam parameter and low ambient temperature.Some other part-load performances and quantitative rules are summarized as well.