As one of the most important techniques in optical tweezers, two-dimensional array optical tweezers have the widespread applications in nanofabrication and biochip manufacturing. Diffractive optical element is the key device to design array optical tweezers. Combined theoretical simulations using pseudo-random phases encoding through Gerchberg-Saxton (G-S) algorithm with experimental measurements, we find that obvious background noise appears when the regular output distribution is array points. A double amplitude filter is adopted to effectively suppress the background noise and impove the quality of diffraction images. These findings are helpful for designing array optical tweezers in the near future.