Cryogenic optical technology is a crucial support technology for weak target and multispectral infrared detection. In order to achieve precise temperature control and prevent contamination in the cryogenic optical system, it is common to integrate the cryogenic optics with the detectors inside a cryocooler. A specific hyperspectral camera requires the integration of a 320×64 quantum well detector and a 320×64 type II superlattice, co-planarly assembled with dual-band micro-filters to create a long-wave dual-band detection dewar assembly. The required operating temperature for the detector is 40 K, and it is achieved using a pulse tube cryocooler.The dewar adopts a windowless design and is integrated with the cryogenic optical system cryocooler using flexible bellows for hermetic sealing and precise alignment adjustments. Addressing the challenges of three-dimensional assembly of the dual-band detector at 40 K, low-stress assembly of the detector and filters, and efficient heat transfer between the cryocooler and detector, this study investigates the three-dimensional assembly of the detector (Fig.4-6), a heat layer structure for efficient heat transfer at 40 K with low-stress integration with the detector (Fig.7), low-stress filter support (Fig.15), and the coupling between the dewar and the cryocooler (Fig.12). Innovative approaches such as a three-point Z-axis adjustment assembly method, an Al₂O₃ carrier composite molybdenum substrate for the detector, a molybdenum support structure for the integrated dual-band filters, and a coupling method with stress isolation for the cryocooler and detector are proposed.Ultimately, this research achieves a detector flatness better than ±2.06 µm (RMS) at 40 K (Fig.6), low-temperature stress of the detector less than 22.06 MPa (Fig.8), low-temperature deformation of the dual-band filter membrane less than 8.55 µm, and a temperature gradient of 2.6 K (Fig.14) between the detector and the cryocooler. The dewar assembly with a 40 K long-wave dual-band infrared detector has been verified through 2000 hours of continuous operation and 300-on/off cycles, with no significant change in component performance before and after testing, meeting the requirements for engineering applications (Fig.16).