A low-cost transistor outline-CAN (TO-CAN) package, which is combined with flexible printed circuit board (PCB) and hard PCB, has been developed for a optical subassembly module. On the flexible PCB, the transmission line structure used top ground microstrip line, and the wider transmission bandwidth can be obtained. Using ground pads and ground notch technologies, the impedance of connection between flexible PCB and hard PCB was designed to match with the impedances of signal traces of the flexible and hard PCBs. In the TO-CAN package, a TO-46 header was used, and the header needs to closely connect with the flexible PCB. The bandwidth of TO-46 package combined with flexible and hard PCBs can achieve above 23 GHz. The clear transmission eye diagram was also measured, and the rise time, fall time, and -factor of the eye diagram are 13.78, 13.56 ps, and 8.76, respectively. The TO-46 package combined with flexible and hard PCBs has been verified to be suitable for application in optical subassembly modules.