Data center networks are the important infrastructure of the modern Internet and cloud computing. It is critical to achieve load balancing in data center networks for guaranteeing high throughput and improving service experience. The difference between the data center network and traditional Internet is firstly analyzedand the features of data center networks and the facilitation for designing load balancing schemesare concluded. Then, the challenges of designing load balancing schemes are analyzedin data center networks from the perspective of complexity and diversity. Existing load balancing schemes in data center networksare classified into four types, i.e., the schemes based on the network layer, the transport layer, the application layer, and the synthetic designs, according to different modification types. The advantages and disadvantages of these schemes are detailedand they are evaluatedfrom the point of the control structure, the granularity of load balancing, the congestion sensing mechanism, the strategy of load balancing, scalability and the difficulty of deployment. Finally, all load balancing schemes are summarizedand some future feasible directionsare presented.