The purpose of this study to describe the error and to know the cause of student error in solving trigonometric problems based on Newman's Theory and cognitive style. The type of this research is qualitative descriptive research conducted at SMAN 1 Sekampung Udik. Selection of research subjects using purposive sampling selected 4 research subjects with 2 subjects have a cognitive style reflective and 2 subjects have impulsive cognitive style. Data collection techniques used were tests and interviews, while the instruments used were: (1) cognitive style test or MFFT (Matching Familiar Figure Test), (2) trigonometric problem test, and (3) interview guides. The results of this study can be described as follows. ( 1) students who have a reflective cognitive style in solving trigonometric problems tend to make mistakes in the stage of transformation error and process skill error; and encoding error, (2) whereas students who have an impulsive cognitive style in solving trigonometric problems tend to make mistakes in the phase of comprehension error, transformation error, process skill error, and encoding error. (3) The cause of the errors of cognitive and relative impulsive cognitive students are the students can not understand the problem well, forget the formula, less thorough in solving problems, rush in solving problems, not used to write conclusions, and run out of time in solving problems