Using the improved G′/G2 expansion method, eighteen groups of exact solutions for Zakharov equation were constructed. As the result, the hyperbolic function solutions, trigonometric function solutions, and rational solutions with arbitrary parameters were obtained. When the arbitrary parameters in hyperbolic function solutions were taken as some special values, the solitary wave solutions can be obtained. When the arbitrary parameters in trigonometric function solutions are taken as some special values, the trigonometric function solutions can be expressed as periodic wave solutions. It is proved that application of improved G′/G2 expansion method can give some new exact solutions of the Zakharov equation, and increase the scope of the solution. This method has a very wide range of application to fields such as nonlinear optics and quantum optics.