In this paper, we investigate the joint design and optimization of source-channel polar coding with 2m-ary transmission. A joint framework is proposed which includes a source polar code to compress the redundant source, followed by a set of component polar codes over a 2m-ary modulation to protect the source against errors and achieve increased spectral efficiency. We prove that our scheme suffices to achieve the theoretical limit of source-channel separation theorem. For finite-length cases, a joint decoder that exploits both the residual redundancy and channel characteristics is also derived to further reduce the error rate. Simulation results verify the effectiveness of the scheme.