The objective of research was to find out the trigonometry learning difficulty and the solution to the learning difficulty with classwiz fx-991EX help. The subject of research consisted of 96 10th graders of Public Vocational High School 2 Wonosari in the school year of 2017/2018. The research method employed was descriptive qualitative one. The result of research showed that learning difficulty was related to: (a) reasoning & understanding of prerequisite material (geometry and real number operation) including: symbol, distance, Pythagorean theorem, circle, triangle, angle in radian and degree, pi concept, and root form rationalization, (b) reasoning and understanding of function including: representation (numeric, graphic, symbolic/algebraic, verbal), and inter-representation relation, (c) reasoning and understanding of trigonometry function including: definition of function based on unit, definition of function based on right triangle sides ratio, multiple representation and property in trigonometry main function. Data of diagnostic test result was supported with result of interview with informants selected representing any types of error in diagnostic test. Learning difficulty revealed was improved using remedial teaching with casio classwiz fx-991EX help.