This paper presents a fast solution technique for power network observability problem. This method is based on graph theory and provides an efficient way to find the topological observability of power system network for a given set of measurement A power network is topologically observable if it is possible to find an observable spanning tree of measurement graph. The observability problem is split in P-δ observability and Q-V observability by P-δ/Q-V decouple characteristic of power systems. The existence of an observable spanning tree is searched through the methodology suggested in this paper and a conclusion about the observability or unobservability is reached. This solution technique has been successfully tested on the standard IEEE test systems and results obtained are presented for illustration.