Thermal deterioration of rock occurs in tunnel portal section due to temperature fluctuation of rock in high temperature environment in southern China. As heat conduction of fracture tip is nonlinear

a triangular heat source function of fractured rock mass is established based on Green’s function method and mirror image method. Temperature distribution of fracture tip is calculated

and influences of fracture shape parameters and multi-fracture interaction on temperature are analyzed. It is found that the internal temperature of fractured rock mass is higher than that of non-fractured rock mass during solar radiation period. For triangular fractures with the same length

the temperature varies greatly as apex angle of triangle is large. When spacing between parallel fractures or coplanar fractures is small

the superposition effect of temperature of fracture tip is strong

and the temperature value tends to that of single fracture with increase of spacing. The temperature of fractured rock mass transfers faster than that of non-fractured rock mass. Temperature isolines appear around fractures

and temperature around fractures increases significantly. The result provides theoretical basis for thermal stress analysis of fractured rock mass in tunnel portal section in high temperature environment.