With wide applications and technology development of CMOS image sensor(CIS), low power dissipation, high integration and high stability become the development trends of CIS. Low dropout voltage regulator (LDO) owns the characteristics of small area, low power dissipation, low noise and high PSRR, thus it can meet the requirement of power supply. To achieve the goal of CIS onchip power system with high integration, low power dissipation and high stability and to avoid the increase of power dissipation or damage of the chips caused by continue working under irregular conditions, in this paper, a design of LDO for CMOS image sensor is presented, and a protection circuit is added. This protection circuit includes two functions of undervolatge protection and over current protection, and it can control the enable signal of LDO by digital circuits. The schematic of LDO and its protection circuit based on 0.11μm CMOS process were also simulated and analyzed, and the layout of the whole LDO is finished under the same process.