Orbifold theory studies a vertex operator algebra V under the action of a finite automorphism group G. The main objective is to understand the module category of fixed point vertex operator subalgebra $V^G$. We prove a conjecture by Dijkgraaf-Pasquier-Roche on $V^G$- module category if V is holomorphic. We also establish a connection between rational orbifold theory and minimal modular extensions. Our work is based on the previous results on modular extensions by Drinfeld-Gelaki-Nikshych-Ostrik and Lan-Kong-Wen. This is a joint work with Richard Ng and Li Ren.