ObjectivesThis study aims to use accelerometer to objectively evaluate daily physical activity （PA） and steps of single pregnant women， and preliminarily explore the threshold of daily steps in line with the recommended PA during pregnancy， so as to provide PA guidance for pregnant women. MethodsWomen with singleton pregnancies who had prenatal examination in the the First Affiliated Hospital of Sun Yat-sen University from April 2018 to September 2019 continuously wore an accelerometer for 7 days for three times to measure daily PA. A total of 178 cases were included in this study with the average age 30.0 ± 3.0 years. Data were downloaded by supporting software， and the relationship between daily steps and PA （total PA， light PA and moderate PA） were analyzed by linear correlation analysis. Linear regression analysis and receiver operator characteristic curve （ROC） analysis were both used to explore the threshold steps corresponding to the physical activity recommendation. ResultsThere was no difference in daily total PA， light PA and sedentary behavior time during the three trimesters （P > 0.05）. But the moderate PA decreased with the pregnancy stages increased （25.1±16.1 vs. 23.6±16.5 vs. 21.5±16.1，min/d， P = 0.001）. There was a positive correlation between total PA and daily steps during the three trimesters （The correlation coefficients r of the early pregnancy， mid pregnancy and late pregnancy were 0.87， 0.83 and 0.86， respectively， P < 0.001）； and there was a positive correlation with light PA （r of the three trimesters were 0.79， 0.72 and 0.77， respectively， P < 0.001）. The relationship between moderate PA and daily steps during the three trimesters also had similar results （r of the three trimesters were 0.62， 0.53 and 0.55， respectively， P < 0.001）. The thresholds of daily steps to reach the recommended PA during pregnancy in the early， mid and late pregnancy were 10 925 steps， 11 372 steps and 11 170 steps， respectively. According to ROC analysis， the thresholds of daily steps in the three trimesters were 10 856 steps， 10 480 steps and 9 819 steps， respectively， and the areas under the curve were 0.81， 0.73 and 0.74， respectively （P < 0.001）. ConclusionsThe daily physical activity is mainly walking during pregnancy. Based on accelerometer evaluation， daily walking 9 800 to 11 500 steps could reach the physical activity recommendation during pregnancy.