• Design and performance test of the DBR laser in GW detection project TianQin-1. • The DBR laser is a pumping source for the main NPRO laser in final TianQin project. • The DBR laser provided a stable output of 18 mW with a drift of 0.6 mW/h on ground. • The internal temperature of DBR laser was controlled at the mK level. • The DBR laser works well as a direct source in the in-orbit laser interferometer. • The resolution and noise floor of the interferometer were about 25 pm and 30 pm/√Hz. TianQin-1 is a mission in the TianQin project, which uses a single satellite to demonstrate the maturity of the key technology for the space-based gravitational wave detection. The spaceborne laser in the TianQin-1 mission consists of a self-developed DBR one and a commercial RIO one. The DBR laser is also developed as a pumping source for the main NPRO laser in the final solution of TianQin. The two lasers were mutual backups and both passed the environment performance verification. The on ground results showed that the self-developed DBR laser could provide a stable output of 18 mW with a drift of 0.6 mW/h. Meanwhile, the internal temperature was controlled at the mK level. The results of in-orbit experiments show that the DBR laser works well as a direct source of the laser interferometer. The overall displacement resolution and the noise floor of the interferometer was approximately 25 pm and 30 pm/√Hz at 0.1 Hz, respectively, better than the goals of the TianQin-1 mission. [ABSTRACT FROM AUTHOR]