Software industrial practices decouple legacy software systems into microservice architectures to improve software maintainability and to achieve faster market delivery. Evaluating microservice code maintainability during the development is a critical issue, facing the difficulties of multi-sourced data and diverse concerns of maintainability. By analyzing source code, code execution trace, and code revision history, a multi-sourced feature space model is proposed to unify the representation of software multi-sourced data. Based on this model, a microservice maintainability measurement system is established with comprehensive metrics, in terms of the concerns of functionality, modularity, modifiability, and interaction complexity. Accordingly, a tool prototype called MicroEvaluator is also implemented, and experimental analysis is carried out on open-source software systems.