Finding the maximum eigenvalue of a tensor is an important topic in tensor computation and multilinear algebra. Recently, when the tensor is non-negative in the sense that all of its entries are non-negative, efficient numerical schemes have been proposed to calculate the maximum eigenvalue based on a Perron-Frobenius type theorem for non-negative tensors. In this paper, we consider a new class of tensors called essentially non-negative tensors, which extends the non-negative tensors, and examine the maximum eigenvalue of an essentially non-negative tensor using the polynomial optimization techniques. We first establish that finding the maximum eigenvalue of an essentially non-negative symmetric tensor is equivalent to solving a sum of squares of polynomials (SOS) optimization problem, which, in turn, can be equivalently rewritten as a semi-definite programming problem. Then, using this sum of squares programming problem, we also provide upper as well as lower estimate for the maximum eigenvalue of general symmetric tensors. These upper and lower estimates can be calculated in terms of the entries of the tensor.