Small scale Readout Integrated Circuit (ROIC) still remain application requirements because of its lower cost, lower power and smaller structure size. A 128×128 format flexible small pixel ROIC was promoted in this paper. In the 30μm pitch pixel, an integration capacitance high to 2.1pF was realized, so the input charge handling ability can reach to 47 Million electrons. The ROIC can work in both integrate-then-read (ITR) and integrate-while-read (IWR) mode, which is decided by the integration signal. A serial data is used to realize some flexible functions, such as fixed windows select, output number select, anti-blooming and the detector bias voltage adjust. A 64×64 fixed window is selectable combined with the complete 128×128 array. Single output or two outputs can be selected for higher frame rate. By the means of the built-in digital to analog converter (DAC) circuits, the detector bias voltage can be changed from -600mV to 100mV. Some digital control methods are promoted to reduce the power consumption of the whole ROIC.