The present research aims to analyse the cognitive behavior of the subject’s inquiry using PBG (Problem Behavior Graph) in the problem solving process. And, PGB analysis visually organizes and tracks the cognitive change of behaviors. In order to collect basic data for PGB analysis, the study developed grammar inquiry tasks and had 20 secondary leaners to solve the grammar tasks. The data collected from the think-aloud protocol of the subject’s inquiry were analysed through step-by-step process according to 10 levels of analysis frame. Based on the protocol analysis, to clarify and schematize the cognitive behavior in the problem solving process, the study provides polygonal lines and joint-connection as the configuration of PBG. And, especially with the latter, it enables to examine the thinking behavior of the subject at each level of steps. PBG analysis is considered to be a refined way to closely examine the grammar inquiry subject’s behavior which, so far, has been considered as a black box. And it could be used as a basic data that embraces the principles, methods, and realities of grammar inquiry learning.