Background, aim, and scope Enhancement of carbon dioxide (CO_2) in the atmosphere has received great attention due to its potential repercussion on global warming and direct effects on the vegetation, especially with a potential increase in atmospheric CO_2 level from 400 mumol·mol~(-1) to 1000 mumol·mol~(-1) by the end of 21st century according with currents environmental studies. Therefore, development of new technologies on controlled environment conditions are needed to investigate plant response to CO_2 enhancements and its possible repercussion on world food security. Among the controlled environment facilities such as the free air CO_2 enrichment (FACE), soil-plant-atmosphere research chambers (SPAR), and CO_2-temperature gradient chambers (CTGC), the open-top chambers (OTC) are commonly used to control elevated CO_2 concentration for plant science research. In the present study, we aimed to evaluate a modified OTC, designed and constructed based on previous OTC experiences, which provides a precise control of CO_2 under different concentrations, with excellent control of air temperature and humidity. Materials and methods Three parts of OTC chamber structure, control system and monitoring system are improved and upgraded. (1) The modified OTC has a regular octagonal prism structure made of plastic steel 4 mm thick high transmittance glass material, an improvement over the previous system. The structure dimensions are 1.08 m length (diagonal), of 2.78 m diameter, and the inner and outer height (top) of 2.55 m and 2.10 m, respectively. (2) The monitoring system consisted of CO_2 analyzers, temperature and humidity sensors, and a data acquisition system. (3) The control system is also composed by other features like programmable logic controller, GPRS communication module, a touch screen, a micro-relay, CO_2 pressure reducing valves, solenoid valves, perforated windpipes, and CO_2 cylinders. The OTC control system automatically collects and uploads data every six minutes using a system control coupled to the PI regulation mode (Proportional integral controller). A linear controller generates deviation monitoring according to a given and an actual output value. The system is also equipped with a GSM communication module connected with the PLC through the Protocol PPI (Point to point interface) to upload all the data to a web server. The OTC control, monitoring system and the data can be accessed in real time through web browser or mobile App, reducing operation costs and allowing environmental variables monitoring. (4) To test the functionality of the modified OTC, Goji berry (Lycium barbarum L.) plants were grown from May to October on 2017 inside the chambers. Real-time data of CO_2 concentration, temperature, and air relative humidity of the chambers were collected. Results As a result, the average CO_2 levels obtained in the chamber during the study period was 369.33 mumol ·mol~(-1) for ambient conditions, while elevated group 1 and group 2 showed concentrations of 558.35 mumol ·mol~(-1) and 772.71 mumol ·mol~(-1) respectively. The fluctuation for elevated group 1 ranged from 551.82 mumol ·mol~(-1) to 572.40 mumol ·mol~(-1) with a variation amplitude of 20.58 mumol ·mol~(-1). In the elevated group 2, the range of CO_2 concentration was from 756.71 mumol ·mol~(-1) to 779.79 mumol ·mol~(-1) with variation amplitude of 23.08 mumol ·mol~(-1). In addition, no significant differences were found in temperature and air relative humidity among the chambers treatments (p>0.05). Discussion The improved OTC simulation control system can well control the CO_2 concentration to meet the preset concentration requirements.