Based on rainfall enhancement operation records in Zhejiang Province and Doppler radar data, sounding data and hourly rainfall observations from automatic stations as well as MICAPS weather chart from June to November of 2018-2020, the indexes of Doppler radar echo for rainfall enhancement in summer and autumn in Zhejiang Province were researched with the inverse method after evaluation of rainfall enhancement effect in order to guide cloud seeding operation more scientific and reasonable. The results show that the shear line, upper trough and typhoon are the most favorable weather systems for artificial rainfall enhancement in Zhejiang Province, accounting for 28.6%, 21.4% and 21.4%, respectively. According to radar echo and precipitation characteristics, cloud types can be divided into stratiform cloud, cumuliform cloud, mixed cloud giving priority to stratiform cloud and mixed cloud giving priority to cumuliform cloud. Mixed cloud is the most common type for rainfall enhancement, accounting for up to 82.5%. The number of samples with obvious rainfall enhancement effect is small, only accounting for 13.4%. Radar echo intensity, radar echo top, vertical integrated liquid water and thickness of negative temperature layer are valid criteria for operating conditions. The indexes of Doppler radar echo for rainfall enhancement are different in different seasons and for different cloud types. So the indexes of Doppler radar echo and the discriminant equation of operating conditions should be established separately. Unreasonable operation was the main reason why we failed to get positive effect of rainfall enhancement, which accounted for 49.2% of all the samples. Many other reasons leading to failure of rainfall enhancement included but not limited to inappropriate time, position and object. The indexes of Doppler radar echo for rainfall enhancement established in this article are scientific and easy-to-use. These studies have evident significance to command cloud seeding operation.