To meet the miniaturization and reliability requirements of satellite system, a design approach on Ka-band transmitting module with a function of cross-backup was proposed. As required by the project requirements, this paper designs a transmitting module which works at Ka band. With the technology of Microwave monolithic integrated circuit (MMIC), and Micro-packaging process, this module consists of 2 channels of input, as well as 4 transmitting channels of output, each give up to 2W RF power and 15% in efficiency. The module has a dimension of 82 mm × 56 mm × 16.5 mm and the mass is less than 110 g. The component includes multiple unit circuits, such as RF/DC combiner, power amplifier unit, etc., which make a high level of integration as well as heat flux density. A lot of efforts have been put on aspects of circuit, structure, and manufacturing details. The circuit design and assemble parameters are optimized to achieve a good consistency of less than 1 dB in gain between 4 output channels. Secondly, the design of heat dissipation was optimized, to achieve the high reliable characteristic of the module. The work of the paper can provide a good reference for similar requirements of transmitting modules.