The difference wave equation is obtained by the discretization of nonlinear acoustic wave equation in atmosphere with in the second-order miniterm approximation based on the finite-difference time-domain method. And the two-dimensional field distribution of continuous sinusoidal wave vertically or obliquely radiated by a linear array of five monopole sound sources is numerically simulated at the different initial acoustic pressures. A comparison between nonlinear simulation and linear one show that weak nonlinearity has definite and apparent effects on the distribution of acoustic field and focused gain of array, leading the distribution of waveform to be closer to the array and the focusing gain to deteriorate, and that the strong nonlinearity has a strong waveform aberration, because the other waves of non-fundamental frequency appear. No evident distinction is found in the effect between the oblique propagation and the vertical propagation, though less focusing gain and influence caused by strong nonlinearity produced by the acoustic geometric spreading result in more attenuation of axial pressure in the case of oblique propagation.