Aiming to meet the diverse seeding rate requirements of different rice varieties and improve the adaptability of rice seed metering devices to rice seeds of diferent grain types, based on the seeding agronomy of multiple rice varieties, taking four types of rice seeds with significantly different grain types as test objects, based on their basic physical properties, a seed metering device with adjustable opening of ladle-shaped holes was designed. The device adopted a composite structure of hole-type and fluted roller-type. It drived the transverse displacement of the adjusting wheel of the seed metering wheel through a gear-linked spring mechanism, realizing stepless adjustment of the hole opening (0 ~ 14 mm). Based on the three-axis dimensions of rice seeds, the optimized key parameters of the holes were as follows: hole length was 13 mm, width was 6 mm, depth was 4 mm, and a seed quantity adjusting plate ( with a height of 58 mm) integrated with a flexible seed cleaning brush and a guiding tooth structure. A three-factor test was conducted on the seed metering device, and the test results showed that as the hole opening increased (from 0 mm to 14 mm), the average seeding rate per hill of indica rice was increased from 1. 55 ~3.30 grains to 15.95 ~ 23. 09 grains, and that of japonica rice was increased from 1. 89 ~ 3. 98 grains to 16.54 ~ 21.69 grains. When the rotation speed of the seed metering wheel was in the range of 40 ~ 140 r/min, the coefficient of variation of the seeding rate was decreased from 67. 42% to 9. 27% as the opening increased. The seed metering device realized stepless adjustment of 3 ~ 20 grains with a coefficient of variation of 10% ~ 70%, meeting the precision seeding requirements of different rice varieties.