A new independent suspension system was designed to meet the smoothness requirements of all terrain cranes, and smoothness research was conducted. Based on the GB/T 7031–2005 standard, a road surface power spectral density was used to describe random road surface characteristics, and a road surface simulation model was established. Simulation studies were conducted on multiple working conditions at different vehicle speeds and road surfaces. The main focus was on optimizing the smoothness of the acceleration response at the three points of the vehicle center of mass, the bottom of the driver’s cab, and the same tonnage rigid bridge. In addition, a comparative analysis of suspension dynamic deflection and tire dynamic displacement was also provided. The results show that under the conditions of 10 km/h E-Class road surface, 20 km/h D-Class road surface, 40 km/h C-Class road surface, and 80 km/h B-Class road surface, the independent suspension system is superior to non independent suspension systems of the same tonnage in terms of RMS values at the center of gravity, cab bottom, and cab, with an optimization rate of over 12%. Among them, the optimization rate of cab bottom and cab under harsh ground conditions reaches 30%, which can more effectively reduce driver fatigue driving. The optimization rate of suspension dynamic deflection and tire dynamic displacement also reaches over 10%, which can more efficiently reduce the probability of oil and gas suspension hitting limit blocks and improve driving safety. This study provides a certain theoretical basis for the design and smoothness research of the suspension system of all terrain cranes.