Functional form of production under technology gap in the same industry, a less discussed topic in literature, is investigated in this paper. To enrich this line of theories, the technology pattern of production function of public accounting firms in Taiwan under different technology level is examined. The main findings are as follows. Public accounting firms with different technology level show different functional forms of production during two sub-periods of 1989-1995 to 1997-2000. Due to potential structure shift in economy, the functional form of production for large firms with high-tech level resembles variable elasticity of substitution pattern during the former sub-period and is exactly variable elasticity of substitution pattern during the latter sub-period. For small ,firms with low-tech level, their functional forms of production remain to be the constant elasticity of substitution pattern during both sub-periods.