Existing test methods for thick-section specimens (≥ 4[mm]) have not provided precise compressive properties to date for the analysis and design of thick structure. In the current study, the cause of the premature failure for thick specimens (T800/924C and IM7/8552) was identified experimentally and numerically. The premature failure was successfully avoided during compressive testing and the failure mode was quite similar regardless of increasing specimen thickness and specimen volume. Furthermore it was identified that the failure location within gauge section does not have an influence on the compressive strength from the experimental result performed with the unwaisted specimens and the waisted specimens. Finally, clear 1-D thickness and 3-D scaling effects on the compressive strength of unidirectional composite laminates existed. The main factors influencing the effects were due to manufacturing defects such as void content and fibre waviness.