The present invention provides a power network topology analyzing method and an on-line load flow calculating method for an offshore oilfield group. The topology analyzing method comprises the following steps of: reading in a CIM (Common Information Model) file, establishing models of all physical elements, reading in a value measuring file, and providing a measured value for each physical element; gathering all closed switches and judging whether the branch processing is finished, wherein after topology analysis, a power system only includes static models of power system elements, i.e. the power system only includes a bus, a generator, a load, a line, a transformer and an electric reactor, and the connection relationship thereof; and transforming the static models into IEEE (Institute of Electrical and Electronic Engineers) standard format models. The on-line load flow calculating method adopts a Newton-Raphson method to carry out load flow calculation, and comprises the following steps of: reading in data; forming a node admittance matrix; establishing a load flow equation; calculating unbalanced power; establishing a Jacobian matrix; solving a modified equation; and carrying out iterative solving. The power network topology analyzing method and the on-line load flow calculating method provide convenience for more advanced information processing systems, and has the obvious advantages on the aspects of a calculation speed, a calculation scale and convergence .