Fish eggs could significantly impact fish population recruitment. The distribution and variation in the number of fish eggs impacts the dynamics of the spawning ground, which is fundamental for maintaining marine ecosystem balance. Haizhou Bay is an important fishing ground in China, and it is also an important spawning and nursery ground for various fishes. Recently, owing to the impact of overfishing and other factors, the fish community structure in Haizhou Bay changed considerably. Presently, Cynoglossus joyneri is a dominant and important economic species in Haizhou Bay and adjacent waters. Based on survey data in the spawning grounds of this area from May to August in 2014 and 2016-2018, a habitat suitability index (HSI) model of C. joyneri eggs was constructed to analyze its spawning habitat characteristics. A boosted regression tree (BRT) model was used to evaluate the weight of each environmental variable in each month, including sea surface temperature, sea bottom temperature, sea surface salinity, depth, and velocity data. The arithmetic mean model (AMM) and geometric mean model (GMM) were used to build the HSI model, and the model fitness was evaluated by cross-validations. Results showed that the range of environmental factors of C. joyneri suitable spawning habitat was similar in different months, but the weights of environmental factors changed considerably. Cross-validation showed that the GMM performed better in May and July, whereas the AMM produced a better estimation in June and August. Cynoglossus joyneri spawning ground distribution varied in different months, and was mainly distributed in the south of the research area in May, and moved northward from June to August. The scope of distribution also expanded gradually. The results showed that the HSI model could be used to reflect the distribution and variations of C. joyneri spawning grounds in Haizhou Bay and adjacent waters. Therefore, different protective measures could be formulated for reproductive parents and juveniles of C. joyneri according to the conditions of suitable habitats in different months, and consequently could be valuable for understanding supplementary mechanisms and determining effective management measures for C. joyneri.