Automated planning focuses on strategies, building domain models and synthesizing plans to transit initial states to goals. Natural language processing concerns with the interactions between agents and human language, especially processing and analyzing large amounts of natural language data. These two fields have abilities to generate explicit knowledge, e.g., preconditions and effects of action models, and learn from tacit knowledge, e.g., neural models, respectively. Integrating AI planning and natural language processing effectively improves the communication between human and intelligent agents. This paper outlines the commons and relations between AI planning and natural language processing, argues that each of them can effectively impact on the other one by four areas: (1) planning-based text understanding, (2) planning-based text generation, (3) text-based human-robot interaction, and (4) text-based explainable planning. We also explore some potential future issues between AI planning and natural language processing.