Abstract: The off-axis elastic constants theory for composites was applied in the Hedgepeth's model to make the model workable for all cracks with inclined orientations. Then, according to the Griffith energy theory and the test phenomena, a theoretical formula was derived to evaluate the tearing strength of envelope materials with central cracks. The results demonstrate that the tearing strengths are affected by the internal factors (such as the elastic constants, weaving density, etc) and external factors (such as the inclined orientation, crack length, etc). Furthermore, the precision and applicability of the formula were verified with the test result and the other tearing strength theories. Investigations on the tearing strength of envelope materials will provide significant guidance for the strength design and safety assessment of airship structures.