Objective: To investigate the association between habitual reading/writing postures and the co-occurrence of common health conditions (overweight/obesity, visual impairment, hypertension, and scoliosis) and comorbidities among children and adolescents, in order to provide data support for the joint prevention of common diseases and comorbidities among children and adolescents. Methods: From September 2021 to June 2022, a multi-stage cluster random sampling method was used to select a total of 4 577 children and adolescents from 16 primary and secondary schools in Ningxia: Jinfeng District of Yinchuan City, Shapotou District of Zhongwei City, Yanchi County of Wuzhong City, and Pingluo County of Shizuishan City. A weighted complex sampling design was used to investigate the association of habitual reading and writing postures with common comorbidities in children and adolescents. Results: The prevalence rates of common diseases among children and adolescents in Ningxia were as follows: overweight/obesity was 22.87%, visual impairment was 62.52%, scoliosis was 2.30%, and hypertension was 1.30%. The prevalence of multimorbidity (co-occurrence of ≥2 conditions) among Ningxia children and adolescents was 15.95%. Multivariate unconditional Logistic regression analysis showed that frequent/always collapsing waist and sitting forward with head lowered increased the risk of common comorbidities in children and adolescents ( OR =1.90, P <0.05). Compared with the corresponding reference group, male children and adolescents aged 9 to 12 years and boys had relatively lower risks of overweight/obesity ( OR =0.71, 0.70); the risk of poor vision among children and adolescents aged 9 to 12 years, male, and urban was relatively low ( OR =0.59, 0.60, 0.73)( P < 0.05 ). Children and adolescents who often/always sat leaning to the left or right were at higher risk of poor vision ( OR =1.78); urban children and adolescents had a higher risk of developing scoliosis ( OR =3.71); children and adolescents aged 9 to 12 had a relatively low risk of developing hypertension ( OR =0.09), and children and adolescents who often/always bent their backs and sat forward on their knees had a higher risk of hypertension ( OR =5.03)( P <0.05). Conclusions Ningxia has a high incidence of common diseases and multiple diseases among children and adolescents, frequent or always collapsing waist and sitting forward with head lowered is associated with common comorbidities in children and adolescents in Ningxia. Proper postural measures for reading and writing should be carried out as soon as possible to encourage children and adolescents to develop good reading and writing habits for effectively preventing and controlling the occurrence of common diseases.