The calculation of weak interaction rates plays a very important role in nuclear physics and nuclear astrophysics. In this paper, we calculate the electron capture rates of 66Fe in the framework of shell model. We mainly focus on the contribution of allowed transition and forbidden transition to the total rates. It is found that in some astrophysical environments, the forbidden transition is very important in contribution to the electron capture rate, in which the non-unique forbidden transition plays a major role. This is very important for nuclear structures and astrophysics.</p>