We obtain necessary and sufficient conditions for the existence of n-th chaos of the solution to the parabolic Anderson model, where Ẇ (t, x) is a fractional Brownian field with temporal Hurst parameter H 0 ≥ 1/2 and spatial parameters, we extend the condition on the parameters under which the chaos expansion of the solution is convergent in the mean square sense, which is both sufficient and necessary under some circumstances.