The carbon-based perovskite solar cells (C-PSCs) have attracted tremendous attentions due to the low fabrication cost and simple structure by omitting the hole transporting layer (HTL). However, the performance of C-PCSs is still lag behind those of conventional PSCs with HTL. In this work, an innovative C-PSC with a gradient doping absorber is proposed and explored by SCAPS simulation. The effect of different doping gradient, average doping content of gradient doping absorber and interface defect density are analyzed. Through the optimization of the above-mentioned parameters, an efficiency higher than 25% could be realized by using gradient doping of perovskite absorber in C-PSC, which is much higher than the uniformly doped C-PSC, due to the additional electric field introduced by the gradient doping. In addition, dividing the CH3NH3PbI3 absorber simply into two layers with a doping gradient of 300 can also enhance the device performance of C-PSC significantly, which greatly simplifies the fabricating process. This research offers theoretical guidance for the design of highperformance C-PSCs for research and industry.