A semismooth Newton iterative algorithm was presented to analyze the deep groove mechanical seal with elastohydrodynamic (EHD) theory.The iteration system included Reynolds equation,cavitation equation,force balancing equation and deformation equation.With the cavitation area of lubricant film distinguished by FischerBurmeister function,the EHD solution of the mechanical seal was solved by only one Newton iteration loop to find the cavitation area and to acquire the film thickness of end face and distribution of pressure.This algorithm is proved to be high efficient.The mechanism of deep groove mechanical seal was researched by this EHD model,and the impact of three different groove shapes as U,rectangle and arc grooves on the seal property was analyzed.The results show that a tiny circumferential dynamic wedge on the seal face helps the deep groove mechanical seal working in a noncontacting condition.The three stages of the nuclear pump mechanical seal show similar sealing property.The circular groove shows weak dynamic effect if considering mechanical deformation alone.The minimum film thickness of the circular groove is far less than that of U and rectangle grooves while running stably.