The main electrical scheme of a station is principal part of power system electrical connection,and its structure not only determines whether customers can acquire enough electric energy,but also influence economical efficiency of construction and reconstruction of a station.3/2 Connection and 4/3 Connection have been widely used in large scaled station.Three groups of alternative designs are chose in the article,of which the first group is single unit connection,and the other two are combined unit connection,and in each group there are one 3/2 Connection and 4/3 Connection plan.A reliability analysis system of main electrical scheme has been applied,to compare and analyze the reliability and economical efficiency of these two kinds of connection comprehensively.The result involves adequacy,security,economical efficiency indices and sensitivity analysis of component dependability parameter of each design.The result shows both 3/2 Connection and 4/3 Connection has its own relative merits,but 3/2 Connection has well applicability: Failure rate of generation has most obvious influence on reliability of the main electrical scheme.And quantified calculation of reliability is necessary in planning and choice of main electrical scheme of station.