This paper describes in brief the Rhoplus theory in magnetotelluric method. With practical examples, the paper deals in detail with the application of the Rhoplus theory in such aspects as the examination of the consistency between the apparent resistivity and the phase data, the estimation of apparent resistivity and phase value as well as their upper and lower limits at any frequency point, the reasonable piecing of the data collected by different instrument systems, the discovery or correction of curve distortion caused by instrument or software processing, and the understanding of the degree of curve distortion caused by interfering noise.