Micro-gas turbine has drawn much attention to be used in micro grids due to its attractive properties such as light weight, small size, safety and reliability, large fuel range and remote control and diagnosis. Currently used micro-gas turbine transient model follows the constant speed rotor control, which does not match the real micro-gas turbine that may operate in two speed control modes: constant speed control mode and variable speed control mode. Compared with the constant speed control mode, variable speed control provides higher fuel efficiency. This paper builds a transient model based on the variable speed control mode of a single shaft micro gas turbine. In a micro grid, performance of the micro-gas turbine, particularly the load tracking ability and speed adjustment process under different load, is investigated through PSCAD/EMTDC simulation. Simulation results validate the excellent load tracking ability of the micro gas turbine and demonstrate the satisfactory performance of the micro gas turbine working in variable speed control mode.