The injection efficiency of the readout circuit is an important factor that determines the performance of ultraviolet(UV) focal plane array detectors. Based on the equivalent model of the gallium nitride(GaN) based p-i-n structure solar blind UV detector and the capacitor feedback transimpendance amplifier(CTIA) readout circuit, the injection efficiency of photo-generated carrier of the detector was analyzed, then the expression of injection efficiency was obtained. The relationship among injection efficiency and integration time, the equivalent resistor and capacitor of UV detector, the gain of amplifier in CTIA was analyzed. The result indicates the gain of amplifier in CTIA is one of the crucial importance controllable factor that can affect the injection efficiency. Meanwhile, higher injection efficiency can be obtained by improving the gain of amplifier in CTIA. Several amplifiers with different gain were presented, and the CTIA structure readout circuits were made up by using these different amplifiers. A chip was designed and fabricated by using 0.35 μm 2P4M mixed signal CMOS process. The ultraviolet detector was individually connected to the CTIA readout circuit with different amplifier gain and the test was carried out. Then the theoretical analysis result of injection efficiency was compared with the testing results. It indicates that the theoretical analysis of injection efficiency agrees well with the actual experimental test result.