Abstract: The occurrence of the unprecedented heavy rainfall in Henan Province during 4-8 August 1975 ("75.8" rainstorm in short hereafter) has passed for 40 years. It has made a deep imprint for us. This event of heavy rainfall produced downpour of the total amount of precipitation of 1605 mm during three days (5-7 August 1975) in a local area of southern part of Henan Province, with rainfall intensity within 1, 3, 6 and 12 h breaking historical records in China. Due to collapse of dams of many reservoirs, about 26000 people were killed by the abrupt floods and huge economic losses were made. During the past 40 years, the research and prediction of heavy rainfalls have made significant progress, one important cause, among others, is the impetus of valuable experiences and lessons that we learnt from this unusually strong rainstorm. For many years, with this event of mega-rainstorm and flood as reference, we have been continuously promoted and encouraged to endeavor toward a higher goal in the areas of research and prediction of heavy rainfalls. For this purpose, the present author has made this review and assessment to memorize the follow-up research activities undertaken in hard conditions during that time period by the old generation of Chinese meteorologists and excellent achievement derived by them. Even for today, many of them are of innovative significance and can be regarded as a substantial or milestone success. The paper will assess the following five key scientific issues: (1) the observed precipitation amount and extreme values of the "75.8" rainstorm, (2) causes of occurrence of the "75.8"rainstorm, (3) dynamical and diagnostic analysis, (4) mesoscale analysis and its important role, and (5) topographic amplification effect. It is my hope to commemorate the 40th anniversary of the occurrence of the "75.8" rainstorm with the paper, and to pay tribute and memory to all predecessor scientists who engaged in research activities of the "75.8" rainstorm.