Abstract: The observation data quality of Mi8 smartphone with external low cost spiral antenna is studied, and the analysis and evaluation are carried out from the aspects of carrier to noise ratio (SNR), pseudo-distance residual, phase residual, etc. The results show that the carrier to noise ratio of original Global Navigation System (GNSS) observation value of Mi8 smartphone with external antenna is about 10 dB-Hz higher than that of mobile phone with internal antenna. And the carrier to noise ratio level is almost the same as that of the measured receiver. Pseudo range residual within 5 m, phase accuracy within 3 m. Different from the mobile phone with internal antenna, the pseudo distance residual of the mobile phone with external antenna has strong correlation with height angle and carrier to noise ratio. On this basis, two kinds of weighting models based on height angle and carrier to noise ratio are given, and real-time dynamic (RTK) positioning performance tests are carried out in static and dynamic environments based on the extended antenna of Mi8 mobile phone. The experimental results show that the RTK positioning accuracy of Mi8 mobile phone with external antenna can reach centimeter level in both static and dynamic environments. Moreover, using a random model based on carrier to noise ratio weighting has higher positioning accuracy in dynamic scenarios compared to a random model with height angle weighting. Specifically, it has an accuracy improvement of about 16% and 50% in the horizontal and vertical directions, respectively.