To distinguish the different reliability and quality of the high power laser diodes facilely, efficiently and nondestructively, some high power laser diode devices were measured and studied with electrical and optical derivative techniques. The results show that the value of junction voltage saturation is a valuable parameter. It closely relates with the quality and reliability of the high power semiconductor laser. The devices with poor junction voltage saturation have so certain defect. For a certain kind of devices, the values of junction voltage saturation are in a certain range. And the device with the values overstepping the range is an unqualified device. Thus, the h value of the dip at the threshold is a valuable parameter to judge the device quality. Furthermore, the laser diode array simulated with shunt-wound laser diodes was measured. The relation between cells which compose array laser and array laser itself was studied. The results show that the junction voltage saturation of the laser diode array is correlated closely with the uniformity of its cells. If the uniformity of the cells composing the laser diode array was bad, the laser diode array itself is sure to have poor junction voltage saturation.