A bomb-borne MEMS gyro drift fast estimation algorithm of airborne smart bomb (SSB) for aircraft was presented to solve the large MEMS gyro error. Firstly, simplified MEMS gyro error model had been established, HMM/RLS no-delay pretreatment algorithm of gyro drift had been presented to solve the conflict about time delay and bandwidth of FIR or HMM/KF method. Then, the parameter difference due to MEMS measurement error and fix error angle of aircraft and bomb, which could be utilized to reckoned the rapid 2 points estimation algorithm of MEMS drift. The MEMS drift could be estimated and compensated in 2.5 s based on the presented method, and the accuracy can be obtained up to 90 percent. The simulation and experiment result proved that HMM/RLS method was a non-delay drift processing method, which could make a balance between the time delay of filter and bandwidth of signal.