M-layer,the tropospheric propagation effect prediction program is revised for greater accuracy, speed and stability. This is achieved through converting the extended complex number representation into the representation by complex exponent, improving the accuracy in Airy function computation, introducing a new mode locating algorithm and implementing a consistency checking procedure for determining the proper method to evaluate the height gain function. The revision has been documented and the new program source code has been delivered. It is recommended that the mode search protocol, not just the mode locating algorithm introduced in this revision, be completely revised. Unlike the current approach of blanketing the whole possible region until exhaustion, modes should be searched according to their range attenuation rates one by one along a well defined path. this should result in a faster and even more stable program. The program size can also be reduced.