Thermally induced magnetization switching (TIMS) relying solely on a single laser without any applied magnetic field is a key research direction of current spintronics. Most studies on TIMS so far have focused on GdFeCo with Gd concentration above 20%. In this work, we observe the TIMS at low Gd concentration excited by picosecond laser through atomic spin simulations. The results show that the maximum pulse duration for switching can be increased by an appropriate pulse fluence at the intrinsic damping in low Gd concentrations. At the appropriate pulse fluence, TIMS with pulse duration longer than one picosecond is possible for Gd concentration of only 12%. Our simulation results provide new insights for the exploration of the physical mechanism of ultrafast TIMS.