This article describes a 1397 nm narrow-linewidth-filter-type external-cavity semiconductor laser (IF-ECDL) suitable for spaceborne strontium clock ultra-stable laser sources. Effective suppression of technical noise, such as mechanical vibration and temperature fluctuations during laser operation, has been achieved by designing an integrated laser configuration and using an invar-based external cavity. The linewidth of the proposed 1397 nm laser is measured as approximately 6 kHz, which is close to the linewidth limit determined by the current source noise of the laser. It is the narrowest linewidth of discrete-device-type ECDLs reported heretofore. In addition, the laser can output optical power higher than 60 mW and provide a mode-hop-free frequency tuning range of more than 11 GHz with only piezoelectric transducer (PZT) scanning. Furthermore, it has quite high power and frequency stability. In addition to satellite-borne optical clock applications, this laser is also expected to become an ideal light source for the fields of precision measurement, quantum physics, and other applications that require narrow-linewidth laser light sources.