Abstract: In order to forward and inverse faster and more accurately in transient electromagnetic methods, the translation algorithm and kernel function algorithm to calculate the apparent resistivity for central loop are studied in detail. The facts that the analytic expression curve in homogeneous half space for lager fixed loop has translation characteristics and kernel function characteristics. The all-time apparent resistivity for the large fixed loop can be calculated by using translation algorithm and kernel function algorithm. A new calculation equation of all-time apparent resistivity for large fixed loop is derived through the mathematical formulas. The operation speed and the percentage error are comparative analyzed between the translation algorithm and kernel function algorithm through the 3 layers K and 4 layers KH geoelectric models theoretical calculations. The operation speed of the translation algorithm is 0.140 6 s, and it's root mean square error is 1.824%. The operation speed of the kernel function algorithm is 3.241 8 s, and it's root mean square error is 0.728%. The advantages and disadvantages of the two algorithms in calculating the all-time apparent resistivity for large fixed loop were given in this paper.