An experimental study is reported on flow boiling heat hansfer of HFC-134a in the entrance section of horizontal smooth tube. The experimental data have been discussed,and a comparison has been made between experimental data obtained and heat transfer correlations. It is found that the heat entrance effects exist in horizontal flow boiling. The analysis shows that heat entrance effect changes with mass rate, quality and heat flux. The heat entrance length is longer than that of single phase flow. The Dembi correlation is proposed to calculatc the average heat transfer coefficient at entrance section.