With the improvement of the fabrication technology in quantum-dot lasers, the characteristics are further understood. In this dissertation, we focus on the phenomenon of simultaneous two-state lasing and mode anti-competition in the designed quantum-dot lasers. The InAs/In0.15Ga0.85As/GaAs laser diodes are fabricated with standard processing techniques. The fabricated devices are bonded on the copper heat sink, and their electrical and optical properties are measured. The measured results show that devices with variable lengths emit light at different wavelengths. In the longer devices, the output spectrum exhibits ground state transition; in the shorter ones, the output spectrum exhibits excited state transition; while the device length ranges between the longer ones and the shorter ones, the laser diodes exhibit simultaneous two-state lasing. Focused on this phenomenon, we observe the spectrum-versus-wavelength curves and the trends of ground state and excited state under pulsed and continued-wave operations respectively. Experimental results show that there exits two peaks in ground state and excited state separately. With the help of external cavity, we prove that the two peaks in ground state and excited state have relationship. In addition, the simple sub-linear curves are used to fit the bandwidth trends in both states under pulsed and continued-wave operation. At the end of the chapter, the two-state carrier and photon rate equations are listed to simulate the two-state light-current characteristic curves. The paper results are added after the simulation to explain the decay of the light power in the ground state. In the 1st part of mode anti-competition－controlling the long-wavelength mode, we found that the nearly lasing peak will appear corresponding to the excited state transitions when the tuning wavelengths locate at 1235nm and 1265nm in the tuning experiments using the external cavity. Simulation of the carrier distribution shows that the carriers in the excited state will increase with the feedback intensity of light at 1235nm and 1265nm from the grating in the external cavity. Carrier increase results in the gain increase in the excited state. As a result, the nearly lasing peak will appear corresponding to the excited state transitions in the output spectrum. In the 2nd part of mode anti-competition－controlling the short-wavelength mode, one facet of the device is anti-reflection (AR) coated. After coating, the device operates in the external cavity. The external cavity laser is controlled to operate at two wavelengths at 1170nm and 1250nm. Three sets of experiments are done separately under different injection currents to study the anti-competition phenomenon. Finally, we compare our results with previous experiments of anti-competition in non-identical MQW lasers. The comparison includes the difference of gain medium, the difference of anti-competition, and the difference of optical pumping in QD and QW lasers.