High quality crack-free Ga-rich Al26.1Ga73.9N film was grown on trapezoidal patterned GaN template (TPGT) by low-pressure metalorganic chemical vapor deposition. The super-short period AlN/GaN superlattices structure was used to grow AlGaN material instead of the direct growth method. We obtained large lateral to vertical growth rate ratio larger than 4.79. The growth rate of GaN layer was proved to be the decisive factor of the lateral to vertical growth rate ratio. Moreover, for AlGaN growth, we found that that the TPGT is more beneficial to suppression of crack and relaxation of biaxial tensile strAlN than planar GaN template. The obtained results demonstrate that, comparing with AlGaN grown on planar GaN template, the threading dislocation density in AlGaN grown on TPGT was reduced from 2 x 10(9) cm(-2) to 2x10(8) cm(-2).