Polystyrene (PS) possesses numerous remarkable properties like high transparency, impressive mechanical strength, and a large specific surface area, making it an excellent mask plate or template for the preparation of anti-opal structures. Moreover, it should be noted that PS also exhibits exceptional nonlinear properties due to the subwavelength periodic configuration. In this paper, a self-assembled PS microsphere photonic crystal saturable absorber (PSM-SA) has been proposed and fabricated. It exhibits impressive properties including high stability, high damage threshold, high refractive index, and large specific surface area. It is suggested that the periodic structure of PS in the film has a significant impact on the photonic band gap, resulting in excellent adjustable optical nonlinear characteristics. By integrating PSM-SA into a self-built ring fiber laser system, a Q-switched laser with a pulse width of approximately 2 μs and a repetition rate of 40 kHz at a wavelength of 1562 nm is obtained. These findings demonstrate its potential for enabling efficient and adjustable nonlinear optical functionalities in various optical devices, contributing to the expanding realm of PS microsphere photonic crystals and their significant impact on advancing nonlinear optics technology.