Parallel used MOSFET exists uneven distribution of the current phenomenon,in order to reduce the harmful in-fluence of uneven distribution,people only can determine the circuit parameters through experiments.The paper analyses the characteristic parameters of MOSFET and effects of circuit parameters on the static and dynamic drain current uneven distribution conditions with math ways in detail,derives precise formula which reflects the extent of malddistributed drain current and effects extent to drain current increasing speed,for reducing the actual work in the current impact of uneven distribution provides a theoretical basis.