Aming at the polarization-dependency issue of grating couplers, standard and improved polarization-insensitive gratingcouplers are successively designed on the thin film lithium niobate（TFLN） platform. During the design process, the particle swarmoptimization （PSO） algorithm is first improved, and then the improved PSO algorithm is used to optimize the grating parameters,including critical parameters such as grating period, duty cycle, etching depth, and incident angle. Finally, a polarization-insensitivechirped grating coupler is designed, and the effective refractive index is adjusted through linear chirp, significantly improvingthe coupling efficiency and polarization-insensitive bandwidth. The simulation results show that the coupling efficiency is thehighest at the wavelength of 1 544 nm, and the coupling losses of the transverse electric（TE） and transverse magnetic（TM） modesof the polarization-insensitive chirped grating coupler are -4.88 and -5.05 dB, respectively. The polarization-dependent loss（PDL）is less than 0.5 dB within the wavelength range of 1 500 nm to 1 580 nm, and the polarization-insensitive bandwidth is 45 nm.