Mesoscale eddies are important in transporting oceanic energy and matter. We investigated the three dimensional structure of an irregularly shaped warm eddy using three Chinese underwater gliders and satellite data during May 2015 in the northern South China Sea. The warm eddy lasted for 2 months, and remained quasi-steady with a mean radius of ~70 km from May 10 to May 31. Along the two glider tracks, the heat content had a big difference of 2x109 J/m2/span which induced an imbalance of the geostrophic/tangential velocity. The geostrophic/tangential velocity decreased/increased with depth within the warm eddy. The maximum tangential velocities calculated from the two gliders were 0.8 m/s and 0.25 m/s, respectively. This confirms that the warm eddy was horizontally asymmetrical. Large errors could be generated when estimating transports of heat, energy, or matter for an irregular shaped eddy using a regular circular model. We suggest that more and better-designed intersecting glider tracks should be used to retrieve the three dimensional structures of eddy. The irregular shape of the warm eddy was likely induced by the oceanic currents, such as the wind-induced Ekman current. Further study is needed to reveal the eddy-current interactions and the mechanisms thereof.