In software project management, it is a useful method to control the progress of the project through effort estimation. How to estimate the effort in real time in the Agile software development has always been a difficulty faced by Agile teams. Aiming at the current mainstream Agile Software Development techniques, Scrum framework, this paper puts forward the calculation approach for reliability of Scrum team members and the Sprint development time estimation approach based on individual reliability, i.e., the total working time estimation of the next Sprint is realized by estimating and adjusting the working time of the team individuals. 51 development teams with 5-9 people have put this method into practice for experimental verification, and the results show that the highest estimation accuracy of this approach can reach 84.1%.