Method and apparatus for controlling combustion of engine having mixed combustion mode with diesel and gasoline

A method and an apparatus for improving unstable ignition and knocking which may be generated in an engine to which a diesel-gasoline mixed combustion mode and a gasoline mixed combustion mode may be applied to low load and high load driving zones may include determining a combustion mode according to a current driving state of the engine from the mixture combustion mode and the gasoline combustion mode, and variable-controlling the compression ratio to a compression ratio corresponding to a corresponding combustion mode by controlling a variable compression ratio device for the control of the compression ratio to the compression ratio corresponding to the combustion mode according to the current driving state of the engine.