Single‐frequency (SF) Precise Point Positioning (PPP) is a promising technique for real‐time positioning and navigation at sub‐meter (about 0.5m) accuracy level because of its convenience and low cost.With satellite orbit and clock error being greatly mitigated by the precise products from the International GNSS Service (IGS),how to deal with ionospheric delay becomes the bottleneck of SF PPP users.Basically,there are five commonly used approaches to mitigate ionospheric delay in SF PPP: (1) broadcast ionospheric model in Global Navigation Satellite System (GNSS) navigation message; (2) global ionospheric map released by the IGS; (3) local ionospheric model generated using GNSS data from surrounding reference stations; (4) satellite based ionospheric model; (5) the parameter estimation method.Those approaches are briefly reviewed in our contribution and the performances of some classical ionospheric approaches for SF PPP are validated and compared using GPS data from two networks in China and the Netherlands respectively.Validation results show that a set of reference stations is critical for SF PPP with sub‐meter positioning accuracy,especially in China.It is better to model the ionospheric delay in a satellite by satellite mode rather than integral mode under the assumption of a thin‐layer ionosphere.Comparing to GIM,the suggested approach,satellite based ionospheric model (SIM),can improve the horizontal positioning accuracy of SF PPP from 0.40m to 0.10m in China and from 0.20m to 0.05m in the Netherlands,while it can improve the vertical accuracy from 0.70m to 0.15 (China) and from 0.20m to 0.10m (the Netherlands).Furthermore,the recommended ionospheric model has been applied to GPS/BDS data for SF PPP as well.The experiment in Beijing shows that the positioning of about 0.5m accuracy can be achieved by single epoch SF PPP based on a reference network of about 40km inter‐station distance.The accuracy of SF PPP based on an accumulation of 10‐15 minutes of observations in dynamic mode is about 0.04m (horizontal) and 0.04‐0.08m (vertical) using only GPS data,while it is about 0.03m (horizontal) and 0.03‐0.06m (vertical) by combining GPS and BDS data.