5th-Generation (5G) fronthaul is an important part of the bearer network. High-precision time synchronization and massive connection requirements may have higher demands on the access network. In order to solve the problems of fronthaul dumb resource management and optical fiber resources, China Mobile proposed a Medium Wavelength Division Multiplexing (MWDM) fronthaul solution. In view of the demand of MWDM scheme and the need to reduce the cost in the implementation of 5G fronthaul, a 25 Gbit/s Transmitter Optical Subassembly (TOSA) for MWDM optical module is proposed in this paper, which is packaged with low-cost and hermetic coaxial structure. Built-in thermo electric cooler is also used to support the harsh conditions of outdoor scene. This paper mainly introduces the key design and packaging form of TOSA, and optimizes its temperature control ability from the design and process. Finally, the photoelectric performance, temperature control ability and transmission performance of the sample are tested. The results show that the device has excellent performance, which also meet the SFP28 package form and IEEE 802.3 protocol standards.