Abstract: There is considerable discrepancy between the computational result of conventional formula and the measuring result on parametric acoustic array length. Aiming at these situations, the array length would be calculated by the numerical method of KZK (Khokhlov-Zabolotskaya-Kuznetsov) equation's numerical solution. Array lengths of the diffusion-limited source in water are measured in tank experiment, and the numerical calculation results agree with the measuring results. The cause why the computational results of using the effective array length formula cannot match with experimental results, but the numerical result of KZK equation can, is found. Finally, the change of parametric acoustic array length with different transmitting voltages is analyzed.