An improved indirect scheme for laser positron generation is proposed.The positron yields in high-Z metal targets irradiated by laser produced electrons from near-critical density plasmas and underdense plasma are investigated numerically.It is found that the positron yield is mainly affected by the number of electrons of energies up to several hundreds of MeV.Using near-critical density targets for electron acceleration,the number of high energy electrons can be increased dramatically.Through start-to-end simulations,it is shown that up to 6.78 × 1010 positrons can be generated with state-of-the-art Joule-class femtosecond laser systems.